Strange 4WD issue- stuck? No, not stuck... this time.

[DevGau614]

I've had a strange issue with my 4wd for some time now. Everything moving forward is intermittent unless I specify otherwise. It first starts off as the 2Hi indicator is blinking. Then, one day, I will just be stuck in 4Low. I'll turn the car on and off for a while, flip through the selector (while car is off to clean the connections), and after about 5-20 mins , it will at least be out of 4Low. Now, the light is acting very strange, and if I could post the video, I'd show you. It basically is just scrambling between off, on, and blinking. Ive taken it to my mechanic and the problem will go away for a few months, but then come right back- and now its coming back faster and faster.

Now the Check 4wd light comes on- but sometimes, it comes on while nothing is acting odd, the car is driving fine, and the light is not even blinking.


can you help me with my problem? I dont want to suggest any thoughts on what it could be, I just want your suggestions- and Im NOT taking it to my mechanic again

 

[IllogicTC]

I'm smelling either a faulty TCCM or a serial data issue, but serial data tends to turd up stuff like the instrument panel (at least seen more reporting this than other things). Really, TCCM almost sounds like a non-starter to me as it seems at least 1/4 of members have had to replace theirs at some point. Must be a horribly-designed circuit or just put in a position where it can't properly shed heat, or something. But that's just my thought, I'm sure someone else may come up with something else.

And what do you mean by "stuck in 4LO?" Do you mean you're actually like IN 4LO, where you're going like 5 miles an hour, or it just SAYS you're in 4LO?

Any chance you have a buddy with a high-end scan tool like a Tech II or one of the fancy Autotel(?) or Snap On units? There's likely codes that a standard "engine code and sometimes ABS/SIR" scanner isn't going to read when that service light comes on. If we could get the codes it would help IMMENSELY, but they aren't always necessary for final diagnosis.

 

[The_Roadie]

Also a possibility s the switch. GM redesigned it in 2005, and the new ones are surprisingly affordable even at the dealer. The way to tell a new one is if it has an up arrow for HI. They pry out from the front. I'd try that first.

Welcome! Glad you found the party.

 

[IllogicTC]

Also a possibility s the switch. GM redesigned it in 2005, and the new ones are surprisingly affordable even at the dealer. The way to tell a new one is if it has an up arrow for HI. They pry out from the front. I'd try that first.
Welcome! Glad you found the party.

IN 2005, FOR the 06 model? Because I don't have the arrow version in my 05. Built in December 04.

 

[The_Roadie]

IN 2005, FOR the 06 model? Because I don't have the arrow version in my 05. Built in December 04.

The exact month of changeover has always eluded me. Might have been mentioned in a TSB, O Master of the TSB Data Base.

 

[IllogicTC]

The exact month of changeover has always eluded me. Might have been mentioned in a TSB, O Master of the TSB Data Base.

I can't recall if I have one regarding this particular issue. I may have not collected it yet. Also need to get those moved to the TSBs in the Resources section sometime and add actual titles.... lol

 

[freddyboy61]

Since the OP has a 2002 model, would one suspect the TCCM as well, given that year's history of flakyness?

 

[The_Roadie]

Since the OP has a 2002 model, would one suspect the TCCM as well, given that year's history of flakyness?

I would if he had reported the specific 2002 flakiness I know about, which shows up as a totally dark mode switch (no lights after the initial lamp test - or no lamp test) and may or may not display "Service 4WD" on the dash. It's possible that a 2002 could have some fault in reading the switch position that the other years don't, but I don't recall any. It's usually a failure to wake up and boot itself with the ignition on, and if the PCM can't communicate with the TCCM, that's what lights up the dash light. Good thought, but it can be more subtle than 2002 = bad TCCM.

 

[DevGau614]

Great News Folks! It's NOT the TCCM! How do I know this? Because I just replaced it with one from a 2004 and the problem still persists. The symptoms have evolved now. Now, the Hi2 is on, and the N light flashes- but not always. Sometimes its a fast blink, sometimes, a slow one. Sometimes, I have TWO lights on at once! At this point, Im wondering if I remove the TCCM, if I can just remove the 4WD option totally and just stay in HI2.

Granted, I would like to have the issue resolved so I can use the 4WD... so Im going to lick my wounds, and see if its still under warranty. If so, then I can just have him do it pretty quick and get the issue resolved.

One more little oddity here, when I do take it to the dealer, he put his computer on it, and I can only assume he clears the error registry and the issue goes away for a few months. But rest assured, it WILL come back!

What other suggestions have you??

 

[DevGau614]

And what do you mean by "stuck in 4LO?" Do you mean you're actually like IN 4LO, where you're going like 5 miles an hour, or it just SAYS you're in 4LO?

Yes, STUCK in 4LO and then I have to leave it alone for around 30 mins and then it will start in 2Hi... or at least the 2hi will be one of the two lights iluminated.

Im also curious if Im actually driving this poor rigg in Neutral... and what consequences that may have if I have been- or if it only says Im in Neutral and Im really in 2Hi.... can say I feel a difference in the two if I am.

 

[DevGau614]

Tell me about this serial Data Issue...?

 

[The_Roadie]

You never said you replaced the switch. It smells strongly to me that it's the switch or the wiring from the switch to the tccm. No chance it's a serial data issue.

You cannot drive around in neutral because the tranny would not be connected to the driveshaft. That mode is meant only for flat towing the truck behind a motorhome.

 

[DevGau614]

Cannot, or should not? Ive been driving around with the N light on and the 2HI blinking.

Also, I tried removing the fuse and putting it back in this morning. No issues thus far today...

If the probelm surfaces again, Im at a loss. I cant imagine the switch would be SO intermittent.

 

[The_Roadie]

I cant imagine the switch would be SO intermittent.

You give too much credit to the insane GM design team that many of us characterize as children with too little adult supervision. After living with the platform's quirks for almost ten years, that's why the switch was suggested in my first reply.

Why would you throw in a TCCM and not also a new switch?

 

[DevGau614]

Ugh, this thing needs an option to alter posts... I meant the problem is intermittent. I had the switch changed out already and the problem persisted through 3 switches, one of which was the newer version.

 

[IllogicTC]

Screwed wiring could always be a culprit. What are the chances of tracing the wiring from the switch to the TCCM and inspecting for anything wrong?

 

[DevGau614]

Update: Now the light is just straight out. The selector switch is not even lighting up at all.

Isnt this FUN???

 

[IllogicTC]

Update: Now the light is just straight out. The selector switch is not even lighting up at all.

Isnt this FUN???

I would highly suggest inspection of all wiring. Disconnect the harness at the switch, and at the TCCM, and inspect for damage or corrosion of the pins. Inspect the length of the wire for any shorts/grounding, or other issues.

 

[The_Roadie]

Update: Now the light is just straight out. The selector switch is not even lighting up at all.

If the lights don't even all flash for a second at ignition on time, that's a dead TCCM or the power to the TCCM has gone out. What was its pedigree?

 

[DevGau614]

Ok, here's what I know. I know when I first replaced the TCCM, the problem still seemed to be an issue. So I pulled the fuse. When I replaced it, the system seemed to be fine. Now (and I should specify that my wife drives the car) she most recently reported that the lights are off and nothing, not even the "Service 4WD" light comes on.

Now, given the amount of off-road driving I do, I want to consider the following: If the system is off, and I have no worry of it getting stuck in 4WD, should I even care? Im really inclined to just leave the damn thing be.

 

[The_Roadie]

Does the dashboard "Service 4WD" lamp come on for a second when they all come on for the lamp test?

You can certainly disable the system by pulling fuses, but that would normally trigger the Service 4WD lamp. Whatever you do, don't cease changing transfer case fluid even if you never use 4WD mode because parts inside there are always spinning.

 

[NFLDTrailBlazer]

Sorry for posting so late in this thread but your culprit is the encoder motor sensor, the tccm is acting the way it is because of the reading its getting from that sensor.

 

[DevGau614]

The encoder motor?? Tell me more. Its really a whack situation. The service 4WD does come on at initial startup, as do the lights in the switch. Most recently, I was stuck in 4WD at startup, turned everything off for 5 mins, and then turned it back on and everything was ok. Also, sometimes, I turn on the basic electricity and everything lights up for a second, then the selector switch goes dark.

The Service 4WD does come on regularly, though.

 

[NFLDTrailBlazer]

and it will if the sensor is not completely gone , as long as the resistance is close the tccm will try to go through the motions , but in the end will only make an educated guess , so basically its like rolling a dice lol.

Also do not buy a doorman motor they are faulty from the factory ( the gear reduction is made of white metal and they are prone to breaking)

 

[DevGau614]

Yup, pulled the fuse! Not dealing with this problem. 4WD is not that important to me in summer. Maybe I'll fix it in October or November when I MAY be going up to the snow.