Service 4WD light on 1999 Silverado

[Mosey]

I have a 1999 Chevy Sliverado 4WD pickup with 75k miles on it. On Sunday I was driving around on vacation in Nashville, TN and the "Service 4WD" light came on. I was not in 4WD and didn't notice anything unusual while driving it. I drove about another mile and shut it off. I looked for oil leaks and didn't find any. I restarted it and the light did not come on, but after driving about 2 more miles it came back on. I drove a couple more miles and shut it off. I restarted it and the light did not come on and has not come on again since after driving about another 300 miles. Any ideas about what's going on? The manual just says it means the 4WD may need service. I had it in 4WD about 10 days ago to go across a muddy field and it worked perfect then.

[rocky2]

Assuming you have the push button 4x4 selector, it just may be a loose connection in the dash. Check to see if all the little yellow indicator lights are lit, or if while you're driving, it dims or goes off and on. Also while driving check to see if by pushing the plastic faceplate around the switches the 2wd light flickers or goes out. I had this same problem on my Silverado. The complete dash faceplate just pulls off and two small screws hold the 4x4 switches in.

[MikePA]

Danny, I did a search on the Internet and found the following'

When SERVICE 4WD appears on your Message Center it indicates that there is a problem with your Automatic Transfer Case. The system is designed to catch many problems before they become catastrophic. When SERVICE 4WD appears you should contact your local Chevrolet dealer immediately.

You can find more information in your Owner's Manual on page 2-121.

[Mosey]

Thanks Mike. I found that in the manual too. I'm trying to avoid going to the dealer and paying a lot of money for them to tell me it's just a bad connection somewhere or something, so I thought I'd ask here and see if anyone has had this light come on or not. If the light came on and stayed on, I wouldn't hesitate to take it in for service.

[MikePA]

Did you also find the place that mentioned a service bulletin about this? It wont cost you anything to call a dealer and ask about it. If it really is a problem, the longer you drive with such a condition, odds are the more expensive the repair will be.

From the 2002 Chevy Avalanche Owner's Manual;

"If the SERVICE 4WD message comes on, there may be a problem with the automatic transfer case and service is required. Malfunctions can be indicated by the system before any problem is apparent, which may prevent serious damage to the vehicle..."

<font color="blue">The manual just says it means the 4WD may need service.</font color>
Not to pick nits, but if your manual is the same it indicates there may be a problem, however service is required.

Just trying to avoid you getting into another situation you'll regret (7308 vs BH FEL), i.e., "Why didn't I take the truck in when the light came on?"

[gobbler]

Danny,

Could be one of 3 things:

1. Bad switch as mentioned
2. Actuator
3. Actuator Module

I have a 2003 and the message came on before 500 miles. The dealer's first attempt was to flash the computer, this fix lasted about 50 miles. Mine turned out to be the actuator. The dealer mentioned that this is a common problem and usually flashing the computer fixes the problem

[Mosey]

Mike, No I didn't see the service bulletin. Where is that? I guess I'll call the dealer and ask. Thanks!

[Mosey]

gobbler - What does it mean to "flash the computer"? Is that reprogramming it? What is the "Actuator"? I'm guessing it's the shifter that engages 4WD? What is the "Actuator Module"? Thanks!

[MikePA]

<font color="blue"> Mike, No I didn't see the service bulletin. Where is that? </font color>
Danny, can't remember. I did a Google search on 'Service 4wd' and one of the hits was one of those sites that mentions the title of the Service Bulletin, but requires you to subscribe to see the content.

[JohnMiller3]

<font color="blue">...requires you to subscribe to see the content...</font color>

AllData...

[Mosey]

I tested the 4WD while in the yard. When I was not moving and in neutral, I pushed the 4 High button, nothing happened and the light did not come on. I pushed the 4 Low button and I heard a sound below that I assume was the transfer case switching to 4 Low and the light came on. I pushed the Auto button and heard the same sounds (I assume from shifting back to high range) and that light came on. I pushed 4 High again and the light came on this time. I drove around some and I could tell it was in 4WD by the way it steered when I turned sharp. I switched in and out a few more times and everything seemed to work normally. So, maybe something was just sticking and freed up. The thing I'm not sure about is that the front wheel drive axles turn all the time, even when 4WD is not engaged. I'm referring to the shafts that have a boot on each end (which I assume is covering U-Joints) going to each front wheel. I know this because I had my wife drive real slow while in 2 High and I could see them turning. The front drive axles on my 1989 Suburban do not turn when it's in 2 High. It has a straight axle with automatic locking hubs.

[gobbler]

Danny,

My gut tells me that on your '99, it's the switch. The actuator/encoder problems are more prevalent on '02-03's.

There is a TSB, you might get lucky by searching GM TechLink. (http://service.gm.com:8083/techlink/html_en/) Click on Bulletins. It's not the full TSB document.

If you can find the correct part number, you can buy it from GM Parts Direct (http://www.gmpartsdirect.com/) and save yourself some money.

Jim

[gobbler]

Danny,

Does your truck have Autotrack 4WD??

IF it DOESN'T, the part number for your switch is 15709327, $30 thru GM Parts Direct

Jim

[Mosey]

"gobbler - Does your truck have Autotrack 4WD??"

It has a switch on the top that says "Auto 4WD". The manual doesn't call it Autotrack, it says it engages the front axle but doesn't apply power to the front axle unless it senses a loss in traction. I'm starting to wonder if mine is in "Auto 4WD" when I think I'm in 2 High, since my front drive axles are always turning. Sure wish I'd noticed that before I bought it!

[gobbler]

You've got Autotrac. That's important to know because the diagnosis is different. I still think it's the switch but that part number I gave you before isn't the right one.

GM has had problems with the Autotrac system, mostly electronic. You may have to have the dealer diagnose it for you.

Autotrac is a set-it-and-forget-it 4wd system. You have it correct buy stating the axle is engaged but not activated unless a loss of traction is encountered. It's only available on the 1/2 ton models.

I'll do some more diggin', but I'd bet you'll need to visit a dealer. /forums/images/icons/frown.gif

Jim

[Mosey]

OK, I guess I'll calm down a little now. I called 2 dealerships and told them about the front drive axles turning all the time and they both said it's normal. There is no power to them unless it's in 4WD, but they are supposed to be turning all the time. They said it's that way for the Auto 4WD system.

[TBAILEY]

HAD THE EXACT PROBLEM WITH MY 99 ALSO DEALER
REPLACED THE 4WD SELECTOR SWITCH IT SHORTED
OUT. COST AROUND $150. /forums/images/icons/smile.gif

[gobbler]

Danny,

Let me calm you down even more. I don't want you to feel that the Autotrac system is junk. It's actually very good and works as advertised. Most of the problems that I'm aware of are electronic in nature; bad switch, actuator motor, etc. Granted, these aren't exactly cheap to replace, but I'd much rather pay $200 bucks for an electronic item than &gt;$1000 for a transfer case. I think those Autotrac transfer cases are well over $1000.

My sister has a 2000 'burb w/ Autotrac and running around town with kids and groceries, she has told me more than once that she feels more secure on wet roads. Especially with something that big... /forums/images/icons/shocked.gif

More people actually complain about the noise and vibration that you get with Autotrac than anything else.

Jim

[Mosey]

Jim - Thanks for all the info! Since the light has not come on in over 300 miles now, I'm going to just wait and see what happens for a while. The 4WD is working and I'll be using it on my property in the dirt and grass every once in a while all summer and fall anyway, so I'll see how it goes. If the light comes on again, I'll take it in and get it fixed before winter. So, time will tell if/when I have to do that. Maybe I'll get lucky (for once). /forums/images/icons/smile.gif

[MDSteve]

My buddy has a 99 2500 that has the same problem. The dealer said that it was the module and would be 400 bucks. He continues to drive it and use 4WD when needed. His started out every so often but now comes on after it warms up.

Steve

[jwstewar]

My '99 w/ 67k is doing the exact same thing right now. I've spoken w/ 3 different dealers and a buddy of mine that works on cars and all said the switch. I had my buddy order it for me. List Price was something like $57 and I believe he got it for me for something like $43. Cheaper than a replacement key fob for my wife when my son lost her keys. I haven't stuck it in yet, but it will be easy just to pop the dash and go. BTW, if you do have to order a key fob don't let them tell you it has to be programmed by the dealer. Did mine in under a minute. BTW, my truck does have the Autotrac, 5.3 liter engine, 4L60E transmission, 3.73 gears, and the Z-71 Off-Road Package w/ the 265/75-R16 tires. The dealership will ask for the last 6 or 8 digits of your VIN and get the right switch for you. Now just gotta get mine put in.

[Mosey]

jwstewar - Thanks! Can you report back after you put it in? Is it really that easy to take the dash off?

[rocky2]

Dan, getting into the dash is so simple it's spooky. It's just held on with clips and plastic "fingers". Grab an edge and yank, turn the key to the "on" position to unlock the gearshift, move it down so it'll clear and that's it. "No tools required".

[jwstewar]

I'll see if I can get to it tonight and I'll send you the part number as well and as someone else said just grab it and pull - gently but firmly. BTW, forgot to mention I also have the problems with the lights working intermittently. Didn't think much of it at first until the Service 4WD light came on. Wife said that when it was on it wouldn't go into 4WD, but I haven't noticed that. We actually use the 4WD quite a bit as her parents driveway is gravel and coming from the direction we usually do the truck wants to spin so it is just easier to hit the Autotrac and go up the hill.

Jim

[jwstewar]

Didn't get to install it last night. When I got home wife tried to mow and killed the lawn mower. Had to work and get that start and put away before the storm came (on a side note can't wait to get a tractor). But the Part number is 15709327. I think right now I have might truck scared, I haven't seen the light in probably 3 weeks. So maybe I don't replace the switch I just keep the truck scared. /forums/images/icons/laugh.gif

Jim

[jwstewar]

</font><blockquote><font class="small">In reply to:</font><hr />
IF it DOESN'T, the part number for your switch is 15709327, $30 thru GM Parts Direct

[/ QUOTE ]

I'm confused, that is the part number that my switch has and my truck has the Autotrac. I have the switch here in my hand and that is the number imprinted on the back of it and it does have the Auto4WD button so I know it is the correct switch.

[gobbler]

I goofed. /forums/images/icons/blush.gif When I was doing a part number lookup I must have checked the box for the Autotrac. You indeed have the correct part number for the Autotrac switch.

Jim

[Mosey]

Jim - Are you still relying on the scare technique, or did you put the switch in yet? My light came on again after over 300 miles of staying off. /forums/images/icons/frown.gif

[jwstewar]

Still relying on the scare technique. Mine hasn't been on now in almost 600 miles. If I can get the grass to quit growing and the mower to quit breaking maybe I can get it done this weekend. Seems like if I have a chance to do it we then have a storm that comes through and since I don't have a garage I don't really want to take the dash out of the truck even though it should - should - only be a few minutes.

Jim

[jwstewar]

So much for the scare technique. Might light came on Saturday. Just before that I had a hard time getting the truck to go into 4WD - lights wouldn' t light and front-end wouldn't engage - of course of all times could seem to get the rear diff lock to want to engage either. Finally got both to engage - only after I left a nice little trail on the in-laws driveway. Gotta get that switch put in.

Jim

[Mosey]

Jim - How does your rear diff engage? Is it controlled electronically or does it engage mechanically? I don't have a rear locker on my pickup, but have a mechanical one on my 89 Suburban.

[jwstewar]

It is just the stock mechanical one from GM, but a lot of times you can get it to engage by feathering the throttle. Makes a big difference when it is engaged and when it isn't. If I were off road a lot I would spring for one of the air lockers, but for my needs the stocker works pretty well. At least a lot better than my limited slip I had in my first truck. Every since then I've gotten the factory locker. Not sure where the Limited comes into play in limited slip, but from that experience it should've been called Let It Slip because that is what it did.

[Al_Wa]

Disconnect the negitive terminal of the battery for about 30 seconds. Reconnect and reset the radio.

[Mosey]

Al_Wa - So will that reset the system or something? I have used that method to get my DirecTV working again, just unplugged it for about a minute, then plugged it back in and it was fine. Have you actually had this same problem and solved the problem this way, or are you just suggesting it as something to try before spending the money on a new switch? Thanks.

[Mosey]

Jim - Did that switch come with any instructions? Just curious if it says to disconnect the battery first. If so, based on Al_Wa's post you won't know if it was the switch or disconnecting the battery that solved the problem.

[Al_Wa]

Danny, The "disconnect the negative terminal trick" was a hip shot because its easy to do (if you can figure out how to reset the clock on the radio) I had a similar problem on a Ford Explorer and got zero, zip help from the ford garage. Although the rig worked just fine, they recommended replacing some drive line speed sensors $$$$. While I was waiting for an appointment (2 weeks) I stumbled across a ford discussion thread about a mile long on "those $%#@ blinking lights" per their direction I disconnected the battery cable and "bingo" problem disappeared, and has not returned for about two years. (the clock is still blinking)

[jwstewar]

Hey Danny guess what?
I finally got around to put my switch in. Don't know yet if it stopped the Service 4WD light from coming on or not, but at least my 4wd lights operate properly now. Don't think disconnecting the battery will do any good as I've replaced my battery (it died) and it didn't anything to the light. I took a few pictures for you. Propably took me a total of 10 minutes and that included "play time" in the driveway to make sure it was working. This first picture is the new switch laying on the seat ready to be put in.

[jwstewar]

This is a picture of the back of the new switch.

[jwstewar]

This a picture of the old switch with the trim panel removed. As we said before, just grabbed it and pulled. Turned the ignition on and dropped the gearshift selector to first, turned the 4-way flashers on (to lower the switch), and tilted the will as low as it would go so that I could get it out.

[jwstewar]

This is the switch once I got it out of its little space. It still has the wires connected to it. I was able to just use my fingers to pry the little tabs out that held the switch in place as well as the tabs that held the wires in.

[jwstewar]

This is a link to the switch in operation. Switch in action (http://my.core.com/~jmstewart/MVC-005W.MPG)

[jwstewar]

I've got probably 150 miles on the new switch and several instance of going in and out of 4WD/Autotrac with immediate response from the switch and no sign of the service light - of course I had gone 600 or miles via the scare technique so we'll see.

[Mosey]

Jim - Thanks a lot for the pictures and step by step instructions. The video is neat! How did you do that? I'm going to keep waiting to see what happens with yours now before I spend any money. My light has not come on in over 600 miles. I talked to 2 people who bought 1999 Silverado trucks new and both of them said their light has come on. One guy said it only happened a couple times a couple years ago and he never did anything and it just quit doing it. The other guy said he took his in and the dealer couldn't find anything wrong. He said the light still comes on once in a while, but hasn't come on in about a year.

[jwstewar]

The video was doing using my old Sony Mavica Digital Camera. I bought it in '97 or '98. I liked at the time because most others were serial port connections (USB hadn't really taken off yet) and this one was floppy. Those memory cards at the time were small and expensive. This allowed me just to keep using the old floppy disk and if I went vacation and "filled" my camera I could just go by another pack of disk. Has been a great little camera. Starting to show its age a little bit in quality of pics, but still works great. I think I can get about 63 seconds of video on a single 1.44 MB floppy disk. Unfortunately when I took this video I had already snapped several photos and only had about 400k left so that is why it is only 14 seconds.

[jwstewar]

Approaching 350 miles and not a sign of a problem, still going in and out of 4WD great.

[Mosey]

That's good to hear. I've also put a couple more hundred miles on mine and haven't had a problem. I had a problem with the radio in my other pickup and after a year or so that problem just went away, so the "do nothing" method does work sometimes!

[Mosey]

After about 1200 miles of no "Service 4WD" light, it came on yesterday. I think my pickup just hates big cities as much as I do. The first time it came on was in Nashville, TN and yesterday was in Indianapolis, IN. Seriously, I'm wondering if city type stop and go driving has anything to do with it? It's never come on while driving on the highway.

[jwstewar]

Mine varied. Never did have a rhyme or reason as to why. I've probably got 1500 on mine now and not a sign of of the service light. Do have a couple of other things going on. The truck developed a squeak in the rear. First instinct was brakes. But then decided no it was u-joints. Purchased both. Started to pull the drive shaft. Pulled the cover off the u-joint. They are tight. Dad and a couple of others don't think they are it. I put the caps back on and go ahead and put the brake pads on - BTW, easiest brakes I ever put on. Didn't stop the squeak - at least initially. Since (I just did it Thursday) I've developed a load clicking sound under acceleration. I've also notice the back of the truck bouncing when leaving a light. Now I think I'm going to go ahead and replace the u-joints.

At 70k the rear pads were still in pretty good shape. Could have easily gone farther, I was just trying to eliminate the squeak.

Jim

[Bird]

Jim, you say the u-joints are tight and I certainly can't say where your squeak is coming from, but . . . my brothers used to own a tire dealership/garage and they had a customer who was referred to them by another garage because he had a slight vibration in his pickup truck. He had already been to the dealer, and another independent garage, had the brakes, tire balance, and u-joints checked, etc. and still had the problem. My brother diagnosed the problem as u-joints that were too tight and told him the u-joints needed replacing. The guy was skeptical, and reluctant to spend more money, afraid that wouldn't fix it, so my brother told him what it would cost to replace the u-joints and that if that didn't correct the problem, he'd have new u-joints and not owe a penny. They put the u-joints in, let him drive it, he paid for it and was happy to do so. /forums/images/icons/cool.gif

[jwstewar]

I think agree with you Bird (of course I usually do). Don't know about being too tight or not, but I do know that when I took the caps off, we hit the driveshaft end a couple of times and the driveshaft (aluminum) didn't want to move so maybe we are on to something. I've already purchased them (thinking they were loose), so money isn't the issue. I hate to just "throw" parts at something, but there isn't too many things back there that can make noise. I'm only out about $25 if I put the 2 joints in and it doesn't solve the problem - I would still have the old ones to put back in if ever the need should arise, but I would also eliminate one more possibility. I've thought about taking the rear drive shaft out and put the truck in 4WD and drive it for a couple of miles that way to see what happens. We did that once w/ Dad's old Chevy to diagnose from driveshaft u-joints or front axle u-joints. Turned out it was the axle.

Jim

BTW, Bird nice looking home you are looking at. Good luck w/ it. Hope it goes well for you.

[bgott]

I learned years ago mechanicin' that the only way to check U- joints is to pull the driveshaft so you can move them through their range of motion. If you have a loose U- joint you ran it through the tight, dry (as in no grease) stage ignoring the vibration.

[jwstewar]

Ironically the vibration started last night on my way home. I'll drive the car the next 2 days and I'll pull it Saturday and change. Everybody kept asking me if I was getting a vibration and I kept saying no - because I wasn't. Am now though. Shouldn't be a big deal to change them. Dad build a press a few years ago to keep from having to beat them out.

[jwstewar]

Finally decided to replaced the u-joints yesterday. When we took the drive shaft out. it was the front ones (in the rear shaft) that were bad. Two of the caps were completely dry and the little pins had completely disappeared. On the back one 2 of the caps were pretty dry and it wouldn't have been long. Started to replace with front w/ the u-joints I had picked up from NAPA. Wrong u-joints they were to big. Since NAPA runs their own schedule I then went to advance to get something. Nothing they had in the book was the right size. Ended up having to go w/ ones the book listed as being for the front drive shaft of a Suburban. Good, got 2 of them and went home. Put them in, but couldn't get the drive shaft to stay in place on the rear axle. Turns out the caps that go into the axle are bigger. Had to run back to Advance - just made it they were locking the doors as I got there. Had to get another joint w/ 2 different size caps. Came home, took rear one back out and put the one w/ the different size caps back in. The new ones at least have grease fittings. /forums/images/icons/smile.gif too bad I've either got to get a grease gun w/ a smaller fitting or remove the drive shaft to grease them /forums/images/icons/frown.gif . But it eliminated my squaking, clicking, and my vibration. Drives (and sounds) like a new truck again.

Jim

[jwstewar]

I'm approaching 2500 miles now on mine and I've done some pretty heavy jerking w/ the 4wd (since I replaced the joints even /forums/images/icons/wink.gif ). But I have a 2 things come up. The other day when I was pulling the tractor out I had it in low lock and went back to tractorin'. Wife came down the road said truck wouldn't go out of 4wd. I figured the new switch was acting up. Told her to get out so I could see. Put the truck in neutral and away it went. She was like "What did you do?" - my reply "Put the truck in neutral like you are supposed to do when changing ranges." I've told her that a hundred times. Still don't know how she got turned out of the driveway and going down the road w/o breaking something - this one wasn't the trucks fault. The other one is. I can't get the new switch to put the transfer case in neutral. I tried when we put the u-joints in. Just sits there. I'm not too worried about as I've never used it anyway. If I would have to have the truck towed I would have it hauled on a rollback. At least I don't have an irritating service light on.

Have you decided to do anything w/ yours yet?

Jim

[agcomike]

I had a 96 that would do that then it suddenly started down shifting into 4wd hi and then once going 80 it tried locking into 4wd lo if it had syncronized it'd locked up and probaly flipped or who knows what.

I'm a ase mechanic and determined that the wiring harness near the front axle where it hooks to the harness was getting wet and caused it..

[Mosey]

Jim, I've been pretty busy lately and haven't had time to keep up here at CBN. I haven't had the light come on in a long time, a couple thousand miles of no problems. I also haven't used 4WD in a long time.

[Mosey]

My luck ran out. The light came on today after 2852 miles of no problems. I used 4-Lo in the yard one day last week and then again yesterday. I worked perfect both times and shifted in and out of 4WD again with no problems. I towed my tractor on a trailer about 20 miles this morning, then towed the trailer back empty and shut the truck off and unhooked the trailer. I drove the pickup about 6 more miles, then out of the blue the "Service 4WD" light came on. /forums/images/icons/confused.gif

[retiredforhire]

I have a 2000 Silverado that just exhibited the same problem, but now all lights are out and 4 x 4 doesn't engage. I pulled the switch out, removed the cover, and found pin connector solder joints broken. Could be cause of intermittent. Made that repair but still no lights and no 4 x 4. Any suggestions?

/forums/images/icons/confused.gif res0wjyj@verizon.net

[jwstewar]

If you could find somebody else that had one I would see if I could borrow their switch for about 15 minutes to see if that did anything. Otherwise before I spent too much time trouble shooting for $40 I would replace the switch - as long as you have power at the switch. If no power going to the switch all bets are off and I have no clue.

[Mosey]

Well, it's been over 4 months now and the light hasn't come on. I used 4WD several times through the winter and it always worked perfect. I guess I just won't worry about the light.

[z71likearock]

I've got a 99 Silverado, autotrac, 5.3, Z71, and just today my service 4wd light came on. I wasn't using it at the time so I have a feeling it's probably just the switch also. My truck has over 100,000 on it and this is the first thing went wrong, and this truck hasn't been babied. It pulls my jeep 100+ miles everyweekend, has forged mud holes that would make you think i'm crazy, and then takes me on 1000 mile trips without a bobble. Thanks for your info and i'll keep you informed.

[Ernest]

Thanks for the pics. I removed my switch and took it apart /forums/images/icons/smile.gif When I inspected it I noticed small cracks on the solder joints of the PC board posts which the small harnesses attach to. Both sets of posts had one or more loose solder joints around the harness posts.

The plastic housing of the switch is part of the method used to hold the posts in place and of course the solder as well. The problem I think is when the switch is assembled at the factory and too much force is used to insert the PC board into the plastic housing. If too mch force is used then the solder joints are weak or even cracked and can tend to loosen in time. This can also explain why the switch will work sometimes then just start to malfunction.

I re-soldered the harness posts and re-assembled the switch. Then I installed it and tested. All is working pretty good after about twenty miles of driving. I will let you know if this switch fails.

Regards,

Ernest

[Ernest]

I repaired the posts on my switch and it's working I posted some info earlier on this.

[joemama]

I have followed this discussion for quite awhile now and used the information, advice and suggestions to fix the common, Service 4WD, light problem. My truck is a 1999 4wd Silverado with the 5.3 and autotrack 4WD. I bought this truck used with 50,000 miles on it. It soon developed the same trouble that some of you have experienced, intermittent lights on the switch, poor shifting, and the Service 4WD light coming on. I removed the switch, (it is as easy as discribed) and found the part number on the back. It did match the part number stated earlier, #15709327. Ordered a new one from parts direct, $30 plus shipping, and replaced the switch. It has been 20,000 miles now and no more problems. Thanks for the advice.
The question was asked about how to put the transfer case in neutral. From the owners manual, with the transfer case in 2 HI. Simultaneously press and hold the 2HI and 4LO buttons for 10 seconds. The red neutral light will come on when the transfer case shift to neutral is complete.

[nimmer]

Ernest, I also took apart the 4WD switch and saw what I think is similar to what you described in your post, the terminals look like they are not soldered properly or something caused them to malfunction. I inspected all of the solder joints and the ones that look the most suspect are the group of four joints. The other 8 solder joints look okay to the naked eye but under the magnifying glass I'm not so sure. Did you find the same situation with the group of four versus the group of seven ? Was it difficult to re-solder the posts on only the visually impared posts or did you just re-solder all of them to be sure ?

Thanks for the reply.

[Ernest]

I soldered all of them again. Use a low voltage soldering gun but make sure you get good flow.

Sorry about the daley but I thought better late than never.

[msw5577]

just wanted to say thanks for helping me fix this annoying problem ... and for very little $.

[rhansme]

I had the same problem on my 2001 Silverado. The light has been comming on and off for some time. Today it came on and I thought I would see what happend when I went to 4wd and then back. Well I found out. It stayed in 4wd and would not return to any other position. I tried all the switches to no avail. I removed the battery cable for some time and tried again. No dice. I came back in to the office and read some more here in this forum and went back outside armed with some information on how to replace the switch. I removed the trim plate from the dash. (very easy) pulled out the switch from its spot and checked the wiring. I reseated both of the connectors, replaced the switch and started the truck. It worked perfect. I was no longer stuck in 4X4. I went to GM parts direct and picked up the switch for 33.00. The dealership wanted 75.00 for the part and unknown amounts of money for the labor! Thanks to this forum I gained some good information and hopefully have this thing repaired for good. I'll follow up if it acts up again.

[Fishman]

Just ordered the correct switch for my 2000 model Z71. I've been worrying about this problem for 8 months now and figured it was the switch. We shall see, but I'd bet this fixes it.

[ackelley]

I'm not a big truck or 2WD junky and don't know much about it. In the last couple of years, I've become quite the outdoorsman and bought a 4WD truck for snow sports, hunting, etc. So I'm pleased to be able to read all of your advice.

I've been seeing that "SERVICE 4WD" message for a year now, but it's always been real on-and-off. I figured if I could determine a pattern of when it happens, I might be able to figure out what it was. But of course, it seems really random with no typical pattern that causes it. I also noticed that the 2WD light sometimes shuts off while I'm doing normal driving in town.

This weekend, I really ended up in trouble because of it. I was in the middle of nowhere scouting for an upcoming elk hunt and got myself real stuck in deep sand in 2WD. And the thing wouldn't go into 4WD! I must have pushed that button 100 times before I gave up and decided to hike to the nearest help. Just for kicks, I decided to try one more time before starting to hike and sure enough it engaged...pulled right out.

Then, when I got back to town, the opposite thing happened... it wouldn't switch out of 4WD! I tried pulling fuses, and battery cables and everything to no avail. Finally, after 45 minutes of frustrating madness... it just worked.

I have no idea why it works every 100th time I push the button, but I gotta get this thing fixed before I go out again. This time the story ended happily and I got home ok, but I don't want to risk it happening again with a worse ending.

It sound like I might have the same switch problem and I'd be happy to bay $40 for a new switch.

Do you guys think that is what I should try???

Thanks,
Aaron /forums/images/icons/confused.gif

[ackelley]

By the way... I forgot to specify: 1999 Silverado, Z71, 5.3L, 68K miles.

[jwstewar]

</font><blockquote><font class="small">In reply to:</font><hr />
Do you guys think that is what I should try??? /quote]

Yep. I replaced mine at about 67k now at almost 90k and have seen the light since. Hasn't failed to shift in that time period either. I did take the old switch apart and resolder in the event it does happen again I could swap it out easily, but so far it has stayed in the drawer.

[ackelley]

Cool. I'll try that as soon as I can.

By the way, as long as I've got you listening, maybe you can help me with another problem I am noticing. When I am off road or when I just go over a bump in the road, something in the rear end of the truck makes a clunk noise... almost like something is loose.

Just like I was saying about 4WD, I don't know much about this stuff. I've done a decent amount of engine work, but nothing on suspension or anything.

Any ideas?

Thanks /forums/images/icons/confused.gif

[jwstewar]

I would guess maybe a loose U-joint. Do you ever notice it when you leave from a stop? i.e. leave a red light. There was a service bulletin on these originally when they came out. It felt like the transmission was slipping and then all of a sudden a clank it would start to go. If I remember right the fix was for the dealer to put a special fluid in the tranny and/or transfer case.

[ackelley]

I'll watch it closer when I drive home, but now that you say that it does sound like something that happens once in a while. I'm the second owner. I bought the truck from the original owner about a year ago. Is there a way to find out if that was ever done to this particular truck? Do I just call the dealer? I hope it doesn't cost me a lot...

[Pat]

ackelley, Before you start the vehicle while all systems are cool, slip underneath and grab various portions of the exhaust system and give them a hearty tug, especially the tail pipe. Could be your niose is something as simple as a exhaust pipe hitting on something. Easy to check and its free.

/forums/images/icons/smile.gif Pat /forums/images/icons/smile.gif

[jwstewar]

The dealer should be able to tell you if it was done. You could ask them what the special GM fluid they put in to stop it. You could then just buy that and do it yourself.

[ackelley]

I took the switch out and re-soldered those cracked posts like you guys said, and so far it seems to have done the trick. I'll keep you posted if it gives me any more trouble, but it looks like it's fixed...THANKS FOR THE HELP!!!

[magsters]

I have a 1999 112K mi also with the same problem of the Service 4WD light intermittently coming on..I took it to the dealer and they said nothing is wrong with your 4WD..Is the dash difficult to get off to check the wiring?

[jwstewar]

Magster,

Chances are it is your switch. The dealer can't find it, because the terminals crack inside and sometimes they work, sometimes they don't - that is when you get the Service 4wd light. If you go back and read the entire thread, I've got some pictures on how I replaced my switch almost 3 years ago now - haven't seen the Service 4wd light since. Though we've only put about 20k on it since then. It sits in the garage a lot since we bought the Trailblazer.

[Zosostl]

Hello all. I seem to be having the same problem.. But My truck is a 2003 silverado 5.3 autotrac. It only has 48,000 miles.. maybe it is the switch too?? I sure hope not. when i bought it i opted not to get any kind of extended service warranty. but i'm thinking that with only less than 50K miles it shouldn't have a bad switch?
It only happened today for the first time. I disconnected the negative battery cable and it fixed it for now.. I will keep you posted as to what happens.. for now i'm going to do the forget about it technique and see what happens..

[contactbluebird]

I have just bought a 2000 silverado 4X4. Just a few days of owning it the SERVICE 4WD light came on. I was upset to say the least. I got on the net ( Google ) and searched "SERVICE 4WD" and this sight came up. I read all of the posts about the replacing of the switch in the dash. So I purchased a new switch and replace it and the light has not came back on as of yet (went on a 425 mile trip after the fix). Thanks for all the help! /forums/images/icons/laugh.gif

[jgmont]

Just to follow up on the service 4wd light,I have a '99 Z-71 with 140,000 mi. and the auto trac system.Came across this site through my search engine,and saved me a considerable amount of money.The dealership down here in Alabama wanted $85 just to hook up the diagnostic machine and said the fix would be anywhere from $250-$450.After reading the threads in this forum I went out to the truck turned the ignition switch to the on position and noticed that all the lights on the selector switch did not come on like they should've during the first 2-3 seconds,which is a self test for the unit.Went and pick up a switch at the same dealership for $70.Installed the switch,turned on the ignition switch to the on position all lights came on,drove back home 4wd light hasn't came on.just another reason why I don't trust dealership service departments.probably would've took my money and wouldn't be none the wiser.Thanks!friends.

[Pat]

jgmont, Pretty scary, huh? I have noted that in some cases it is not the dealership at fault, and isn't an under the table policy. In some instances it is the mechanic (can I call them that or do I have to say technician which implies, sometimes erroneously, that they are technical) who doesn't want to draw attention to his shortcomings and does what he has to in order to fool his management as well as the customer. More revenue from them helps them stay on managements good side.

I took my "beater" Dakota into the dealer with inop radio and asked them to have a look. I specifically requested they check all related fuses. I got a huge estimate for replacing it. I declined. A fuse cover was off under the dash near the parking break pedal and a ckt breaker fell out driving rough roads and off road. When I put it back and fussed with all the fuses in the exposed fuse box to make sure they all made contact, the radio started up and has worked fine for a few years since.

I have considerable experience at this dealership and don't think there is systematic dishonesty. I do suspect a tech was less than thorough and or honest in the instance of wanting to sell me a new radio.

Lets assume management doesn't know about your situation. If they don't know. then they can't take steps to correct the problem. You need to to do your part to keep them armed with feedback on which they can base decisions. If you tell them what happened and how you fixed it and they don't thank you and instead give you some s--t and get all defensive instead of being appreciative for your assistance then you have learned a lot and may not want to risk being at their tender mercies in the future.

If we don't speak up and give management a chance to correct problems than we deserve the treatment we get.

Pat

[Louisjohn]

Here in the UK there are a number of RHD Blazers. Unfortunately Chevrolet decided to pull out, leaving the owners unsupported.
I had the service 4WD light come up, and found that apart from the selector switch not working some of the time that the mechanics seemed OK. Looking through various forums it seems that there are two areas to consider. 1. the front axle lock up clutch, which is vacuum activated, it seems that the cable can stick, or the vacuum unit can fail. 2. the 4WD selector switch can have a fault with the pins to circuit board connection. Advice was given on this forum, that one way of checking the selector switch was by pressing the body and at the same time pressing a switch. I tried this on my vehicle and it worked, thereby indicating the unit was faulty. Now comes the fun part! No main dealers in the UK, we have a source for spares from a network called Ampar. Contacted them, yes can get the part, ï½£840, approx $1600. Being of pensionable age this cost was out of my budget to say the least. Eventually I found a US main Chevrolet dealer, who not only would provide, and ship the part to the UK, but would sell it including shipping at one tenth of the UK price. The part was received, and was the correct UK spec. I have fitted the unit, and all is working fine, with no return of the Service light.
If it were not for this very helpful forum, I would have had to consider scrapping a fine vehicle.
/forums/images/icons/grin.gif

[Pat]

I just love it when a plan comes together!

Pat

[jml755]

Hannibal, is that you? /forums/images/icons/laugh.gif

[Pat]

No, I was just channeling Hannibal. Funny how it gave me a vague taste of a cigar...

Pat

[brittanie22]

I was driving up my hill in the snow...and I Pressed the 4WD (4H) to drive in snow and it went in fine ...when I was leaving my house going down my hill I put it 2wd...and the SERVICE 4WD came on immediately after...then I tried to put it back in to 4wd and it doesn't work. so in the snow...im pretty much screwed. How much do you think something like this would cost? /forums/images/icons/frown.gif

[jwstewar]

I think most of us were paying about $60 for the switch. Not sure what is going for now as mine has been replaced for several years now.

[schuenet]

IT WORKS! IT WORKS! IT WORKS!

3 years of intermittent "Service 4WD" light. I pulled the dash and switch using no tools. I pryed the cover off the switch with a small flathead screwdriver. The posts looked fine to the naked eye, but under a microscope, the solder on the posts were definitely fatigued. A quick relfow with the solder gun was all that was needed. I put it back together and it works just fine! $0 spent and only 10 minutes of my time.

Thank you to everyone!!!!!!!

[rcjtplt]

any idea what the cost was?

thanks

[shesuredoshine]

I have an 03 Silverado, Service 4WD Light on. The 1st time the mice chewed the wires by the transfer case. Fixed the problem once the wires were fixed. The 2nd time I checked all fuses, OK, checked all wiring OK, getting power everywhere. I pulled the 4wd switch out, popped it apart since many guys suggested the connector bread and to put a drop of solder on it. Not my problem all my lights were burned so my switch was fried. I bought a new switch $88.00 and nothing worked so I disconnected the battery for 15 minutes and it reset the system and everything is OK. So try the battery disconnect first and save some money but in my case my switch was fried anyway. Good Luck

[blackj]

i have 99 silverado ext cab lt. the service 4wd light is constantly on. before it would switch on and off. ive changed the switch out and drained the old oil out and put new oil in...the light stays on now.. why is that?