Service 4WD light on 1999 Silverado

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.

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.

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.

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.

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?"

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

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

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!

<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.

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

AllData...

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.

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. 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 and save yourself some money.

Jim

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

"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!

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. [img]/forums/images/icons/frown.gif[/img]

Jim

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.

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

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... [img]/forums/images/icons/shocked.gif[/img]

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

Jim

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). [img]/forums/images/icons/smile.gif[/img]

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

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.

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

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".

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

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. [img]/forums/images/icons/laugh.gif[/img]

Jim

</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.

I goofed. [img]/forums/images/icons/blush.gif[/img] 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

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. [img]/forums/images/icons/frown.gif[/img]

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

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

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.

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.

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

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.

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.

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)

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.

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

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.

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.