ABS light and SERVICE 4WD.

[Biomedico555]

First thank you for taking the interest in reading my post. Now,
I have a 2004 Chevy Tahoe z71 5.3 engine. and i am getting an error message that is driving me crazy.
I Go to Start the truck and the abs light comes on and 2-3 seconds later the Red Brake light comes on (next to ABS) and the message SERVICE 4WD flashes on the Information center. At this point the Truck wont even Crank. you turn the key and the dashboard shuts down and it does nothing. !!
Doesnt matter how many times u turn the key same thing happens.
what i also notice is that truck is sitting on 2WD even if i just had it on AUTO when i parked it, and if i try to get it to another mode (4WD L or 4WD H or AUTO) it just flashes and it wont change modes, even though i can hear the transfer case motor making noise as if it is moving gears or something.
Now, i leave it alone for a while, an hour or so and i go back to the truck, put my key in and sometimes the message is gone. At this point just turn the key and it starts right up as if nothing has happened. Now i can move in and out of different 4WD modes.
somtimes message gone in one hour some times i have to wait overnight.

First i thought it was a bad starter. had it replaced, just to have it happen again a few days later.
After reading on the internet i found out that when the computer finds a malfuntion with 4WD system it disables vehicle so u cannot start it. Kind of makes sense cause when message gone vehicle starts right up.

My confusion is from reading so many posts. some say is a malfuntion of the Tranfercase motor (moves truck in and out of 4wd), other say position selenoid, others say there is a bulletin from GM regarding the wires that connect to the transfer case. something about it shorting out due to water damage or dirt.

So i attached a Code reader even though there is no Check engine light on it and it returned these codes:
P0740 P0758 P0785 P2761
Now, that was one of those cheap readers and i read i need a better reader to actually read the transfer case codes. Thats my next step, but i was hoping some one had read or encounter similar problem and can maybe point me in right direction.
I should mention when i look under truck there are no leaks. Other than that truck in excellent condition.

Thanks in advance for reading and trying to help...

 

[clkelley]

Welcome to the neighborhood!

Ok, the first thing you need to do is find someone with a scanner that can scan the "C" codes for the chassis. This will allow them to narrow down the issues a bit with the transfer case.

That being said, although it is common that the dash button will go out, and it will flash like you stated when it goes out, since you are saying you can hear the t-case attempting to engage/change the drive mode, that leads me to believe that the encoder motor sensor inside the transfer case is having some kind of communication failure. That sensor senses what mode the transfer case is in so that the computer knows what to do when you hit the button. Apparently this communication is failing and as a result all you do is hear the t-case trying to do something, it just doesn't know what to do.

Now, there are a couple of things that can cause this. Sensor failure, wiring harness issues, harness plug issues, etc. But to narrow that down you need the C codes to determine exactly where the communication failure is.

Ok, for the ABS and service brake lights. Honestly, if all this started at once, I would tend to think that there is an underlying issue with the ECM or harness, etc that is causing multiple systems to fail.

Please note, none of the issues you are stating would cause the truck not to start. So that is telling me there is something else wrong causing issues with all of this.

Go ahead and disconnect the battery and leave it disconnected for at least 15-20 minutes and then reconnect it. This will in a sense reset the system. You want to find out if it repeats itself. If the lights and codes go away after doing this, or if it fixes the issues, then take it into the dealer and have the reflash the ECM.

If disconnecting the battery has no effect at all, you need to get it to someone who can scan it. This way you know where to begin looking for the problem.

Side note: Make sure you don't have squirrels living under the fuse/relay box under the hood. I have seen many situations where squirrels will make a nest in there or somewhere around some wiring and chew throguh the wiring causing all kinds of problems.

Hope this helps get you started.

 

[the-hoe]

I agree with what was said above (smart guy) I do not really have any additional information, but maybe a question that could lead to an anwser. If there was a fault in the transfer case control module could any of this be a result? i only ask because i had a abs light and a service 4wd light for a long time, and it would be stuck in 4wd sometimes, and fine other times. Once i unplugged the tcm the light was gone and it was always in 2wd. Not an issue for me anymore, just trying to bring up ideas to help the thread starter.

 

[Biomedico555]

Thank you guys for taking the time to repond to my issue. I love my truck and i've own it for about 4 years now and I've never had any issues with it.
The problem is that the issue is been fixing itself in about an hour and the check engine ligh has not come up. However previous time it happened I pull the TREC fuse for about 2 mins ( i read somewhere this should clear the codes) and disconected the battery for about two hours.) That didn't work. i remember getting so frustrated, and after checking all fuses (they were all good) i grabbed the wiring harness by the fuse box and i started shaking them 1 by one (there's 3 of them) at first nothing, but then i shook them again and message and lights were gone and truck started right up.
I didn't think it had anything to do with it because supposedly if there is a SERVICE 4WD message the truck won't start. Can anyone confirm weather this is true or not ??
The issue happened again yesterday morning it didn't start, and i try starting the truck again last night and still wont crank. If in fact a SERVICE 4WD message wont stop truck from cranking then it has to be an ECM issue or wiring harness.
That's actually a good thing because now i could get to the bottom of this. First thing i will do when i get home tonight is grab a hold of those wiring and give them a good tug and see what happens.
I should mention that in order to move the truck yesterday (I live in New York so i needed to move it to the other side of the street due to cleaning regulations or get a $115 ticket YIKEESSS !!), I took a wire from battery to Starter and while ignition switch on the run position I jump the truck, (force the starter to run). Truck started right up but on the "limp mode" like reduce power and i was able to move it across street.
so Tonight i will shake wiring and report my findings..

Thanks.

 

[clkelley]

NO! Don't just go in and begin jerking on the harness, you could make it worse. I tell you what you need to do, go to the local parts store and get some electrical connector cleaner, a small detailing brush and some dielectric grease. Take that home and start at the ECM. Properly remove the plugs themselves from the ECM and clean, dry (with a hair dryer) and grease the plugs connecting lead pins, etc. Once you are done with the ECM plugs, move to the engine electrical grounds and make sure they are not lose or missing and inspect the wiring for damage. Then move to the engine wiring harness and sensors and repeat the process for cleaning and drying them. The move down through to the transmission and transfer case harnesses and do the same thing.

Once you are all done with that, you have cleaned, inspected, dried and greased the majority of the harness and plugs to eliminate a wiring issue. It takes time and patience, but you can do it in one evening and know for sure if it is the harness.

If that proves out not to be the issue then take it in and have the ECM reflashed. This will reset everything in the ECM and the dealer will be able to tell if the ECM is fried when they do the reflash.

 

[Biomedico555]

Awesome piece of advise. I'm hoping problem will NOT go away on it's own so i could do everything as you told me. then hopefully that will do it..
I will take my time so i will wait to Saturday morning so i could do it with daylight on.
Let's get the cleaning products out and let us do dome cleaning.
Great advise !!

Thanks..

 

[E509]

So has anyone found out what needs to be fixed I have the exact same thing happening. Besides mine doesn't start sometimes, it just won't start.

 

[chubbs]

first of all, the "SERVICE 4WD" will not in itself disable the vehicle from starting. I suppose if the issue regarding the 4WD is bad enough like a wheel bearing about to self destruct, the vehicle could disable the starter but I have never heard of such a thing.

I had the "SERVICE 4WD" d.i.c. message last Monday after driving in a terrible storm. It took me several days to diagnose the problem but the vehicle always started, with the SVC4WD displayed, NOT flashing. I eventually found the main transfer case harness full of moisture as result of driving through flooded roads; once it dried out the message was no more. Also, while the plug was wet my transfer case would not do anything when trying to select different modes with the 4WD selector switch. There was no blinking, no motor movement, etc. The 2WD selection was illuminated and that was it. If I had ABS and 4WD warning messages, I would be checking my wheel bearing ASAP as this is the commonality between the 2. Lift your front end up with tires cleared of the ground and check for play in the wheel hubs by attempting to move the tire back & forth @ 6:00 o'clock and 12:00 o'clock. If there is play when moving the tire @ 9:00 and 3:00, it usually concerns a tie-rod end or steering linkage issue.

You very could well have an electrical or sensor fault of some sort that may or may not be resolved via software capable of reading/interpreting GM-specific chassis codes, but please rule out mechanical failures of any sort before you have bigger problems like being stranded in a median on 3-wheels or waiting for a tow truck with your vehicle disabled in the HOV lane. People say that faulty wheel bearings usually give you a warning sign on these models but I have seen some things in my life and tend to check my wheel hubs occasionally as result.