Strange 4wd Issues 2003 Tahoe

awalkertx · December 21, 2009

Here's the info: 2003 Tahoe, 110k miles. I've owned the truck since 25k, and after 50k miles, about once in every 100 starts, the 4x4 mode light will be in the red intermediate mode, and the mode can't be changed with a button push until the truck has been cycled off and then back on.

In the past few months something else has been happening. I'll start the truck, and it goes to auto 4x4. The next time, it's in 4x4 high, or even 4x4 low. If i quickly toggle another mode, it will obey. if i don't do it right away, it will be stuck in that mode until I cycle power to the truck. The truck has always been in 2 high when I shut it off.

I've searched the forum a bit, and can't find issues quite like this. I don't get a "Service 4wd" light on the dashboard if that means anything. The truck is in fact changing 4wd modes... just seems like a gremlin is in charge.

Is it the switch? Until recently, I have never pushed any of the buttons. 4x4 has never been used in this truck.

Thanks for any help you sages can give!

Adam

lvlagnum · December 21, 2009

It MIGHT or it MIGHT NOT BE but part of the problem COULD be your Tahoe's four-wheel-drive has seldom or never been used. Just like the emergency brake and the airconditioning system, the four-wheel-drive system should be used several times a year, even if they're not needed, to keep the linkages freed up and the seals lubricated.

Another possibility could be it sounds like a situation I had with my '03 Silverado Z71. I thought it needed a new switch but when I took it back to the dealer to be repaired under warranty, they said all it needed was to have the PCM reflashed with an update. They reflashed it and I never had that problem with it again.

Please let us know what your particular problem turns out to be.

Cheers, lvlagnum.

PS: Never use four-wheel-drive on dry pavement as it is not good for the system. Find some loose sand, mud or snow to give it some excercise. Just like a loyal dog, a four-wheel-drive vehicle needs to be let loose for a good run every now-and-then.

awalkertx · December 21, 2009

Hola lvlagnum,

I did a little more looking on the forum here, and I decided to pull the switch out of the dashboard and open it up. Several posters have mentioned something about cracked solder joints on the pcb. Everything looks fine, and I'm only looking at the top of the PCB since it didn't want to come out of the back of the housing.

I'm probably not going to re-flow the solders since they look ok (to my untrained eye).

As far as 4x4 not getting used, I should have said that it was never needed. I would say that maybe once a year I would cycle it in and out of the different modes and drive it in a straight line. It does still go through the modes now. I will say that as of a few weeks ago, it is VERY rare to start the truck and not hear it go into something random... usually auto 4wd.

I am, however, interested in what you have to say about reflashing the PCM. Will the dealer be quickly receptive to this idea? I am leary about taking this truck in and getting slapped with a huge diagnostic fee. Is there a tecnical bulletin on this issue? I'd love to go in there armed with as much info as I can.

Incidentally, I am fresh out of the 5 year major guard protection plan I never EVER used. I'm a little miffed as I was deployed at the time when it went out, and I found out when I took it in with a laundry list of things to do. Live and learn!

Thanks for the reply!

Adam

lvlagnum · December 21, 2009

Adam.

I have no idea if there is a formal TSB out on this issue or not. There are members posting on this forum who are dealership service managers, service advisors and service technicians who I'm sure could tell you much more about it than I could. I do know when I took my truck into the dealer, the service advisor knew right away what the likely problem was. That would lead me to believe it's quite a common occurrence.

If you have access to a reliable code reader, I'm sure there must be a fault code which shows up. Ask around and perhaps a member of your family or a friend might have a code reader. If you tell us where you're from, one of the other members of this forum might be close enough to help you out. If that doesn't work, perhaps someone reading this could help out by telling you which brands and models of code readers are the best to buy. I know there a few inexpensive ones which are available at most good autoparts stores.

Please let us know what the results are.

Cheers, lvlagnum.

awalkertx · December 22, 2009

lvlagnum,

Well, as far as I can tell, the switch has nothing to do with it. I had pulled it out last night, and the first time I started the truck this morning... I heard the transfer case change modes. I plugged the switch back in, and sure enough the truck is was in 4x4 low. I guess the next step is to take the truck in. My real fear is having this anomly actually screw something up that isn't yet damaged.

I am uber-poor right now. All I can afford I guess will be diagnostics. Anyone know how much that might run? If they do re-flash the PCM, does that cost extra (on top of the diagnostics)? Would really be nice if GM would treat this like a firmware upgrade and cover it. There's no materials, and really no labor involved. Wishful thinking I guess!

Thanks for any insight anyone can provide. I'm really bummed right now.

hitemup84 · December 6, 2014

I see im not the only one viewing this if you come up with an answer please let us know this is 5 years old now. ... and its the most recent search that pops up on google.

gmtech4 · December 6, 2014

Op, TSBs are not for a truck owner , and it's not free , it's a tip for the tech to fix a veh for a particular problem/ concern ,

Also a code reader will NOT read TCCM codes , will read PCM/ECM Ccdes

When you get the "service 4WD" message that means there IS a code in the TCCM,

And using 4 wd now and again to keep it working is a crook of poop ,

You don't know if the TCCM has the lastest calibration until the scanner is hooked up to the GM system ,

DO NOT jump to any conclusion about your concern especially when funds are less than ample

hitemup84 · December 6, 2014

Ok my truck tonight i put it in 4 low, when it went in it seemed to "slap" into gear, now it wont come out, there is no codes thrown but upon startup the red light next to neutral lights up, tried to rolling front back park neutral etc etc wont come out. I do use my 4wd from time to time but today seemed to be a lot harder then usual.