2002 tahoe z71 Service 4wd light on, no blown fuses, new selector switch.

[Ialsofkdyourdad]

Hey I know this question has probably been asked before but I have been googling all day.



I bought the truck last week knowing it had this problem, previous owner had planned to fix it himself but has been unemployed for month and was clearing out projects. It's a 2002 with no rust ( im in Alberta Canada, that's hard to find) engine is strong so I bought it knowing 4wd wasn't working.



When I got it the service 4wd light was up on the dash and the selector switch backlighting wasnt fully illuminated. And it didn't even light up that it's in 2 hi. So I ordered a new 4wd switch and installed it today and the backlighting works but it still doesn't light up that it's in 2hi, the buttons don't do anything either. I checked the "atc" fuse in the engine bay and the 4wd fuse in the dash, both were fine.



I have been reading that there are ground points for the tcase to check and to check if the tcase motor has power running to it, I will do that probably tomorrow Morning but if it's not that should I buy a new tccm? Should I go to a chevy dealer and try to get it reprogrammed? Or just go to a dealer and get them to diagnose the problem? I'd prefer to just fix it myself but I'm not sure where to start

 

[Doubeleive]

you need to check the encoder motor on the transfer case for operation and the solenoid in the front differential
being the light isn't doing it's thing I would lean more towards the encoder motor, get under there and check the harness at least before throwing any more money at it.
be sure everything is plugged in and clean I had mine worked on once and 4wd wouldn't work afterwards, they had left a harness unplugged.

 

[Scottydoggs]

scan it for codes with a real scanner that does c codes. might have something to go off of there. my 4wd got stuck in 4 low, and it actually set a code for it but it never turned on the cel. found it with the app below.

or this app works well, its free other then a blue tooth obd2 scanner. https://play.google.com/store/apps/...vroletsys.chevroletsysscanfree&hl=en_US&gl=US

 

[Fless]

scan it for codes with a real scanner that does c codes. might have something to go off of there. my 4wd got stuck in 4 low, and it actually set a code for it but it never turned on the cel. found it with the app below.

or this app works well, its free other then a blue tooth obd2 scanner. https://play.google.com/store/apps/...vroletsys.chevroletsysscanfree&hl=en_US&gl=US

Get the codes with a scanner that will read the 4x4 codes and let us know what they are. It's likely the encoder motor or a connection on that, as @Doubeleive stated. If you get as far as replacing the TCCM Dorman makes one, I think, that doesn't require programming, but I haven't heard whether they're good or not. But I'd be checking other things first. A Tech 2 or advanced scanner would be invaluable for troubleshooting this.

 

[Ialsofkdyourdad]

you need to check the encoder motor on the transfer case for operation and the solenoid in the front differential
being the light isn't doing it's thing I would lean more towards the encoder motor, get under there and check the harness at least before throwing any more money at it.
be sure everything is plugged in and clean I had mine worked on once and 4wd wouldn't work afterwards, they had left a harness unplugged.

I have a multimeter is there a list of voltages it's uppossed to have? I'll deffinatly check that out tomorrow and see if anything obvious is bad

 

[Ialsofkdyourdad]

scan it for codes with a real scanner that does c codes. might have something to go off of there. my 4wd got stuck in 4 low, and it actually set a code for it but it never turned on the cel. found it with the app below.

or this app works well, its free other then a blue tooth obd2 scanner. https://play.google.com/store/apps/...vroletsys.chevroletsysscanfree&hl=en_US&gl=US

That app will read the tccm? Everything I have been reading has said only a tech 2 can read it. I can take it to a chevy dealer but if I could scan it myself with a Bluetooth module I'd prefer that lol

 

[Ialsofkdyourdad]

Get the codes with a scanner that will read the 4x4 codes and let us know what they are. It's likely the encoder motor or a connection on that, as @Doubeleive stated. If you get as far as replacing the TCCM Dorman makes one, I think, that doesn't require programming, but I haven't heard whether they're good or not. But I'd be checking other things first. A Tech 2 or advanced scanner would be invaluable for troubleshooting this.

I have read that before replacing the tccm that a dealer can reprogram it or at least tell you if it's the module that has shit the bed. Is this something a used part would work for? I have a few self service junk yards near me and I could pick one up from them for pretty cheap

 

[Doubeleive]

I have a multimeter is there a list of voltages it's uppossed to have? I'll deffinatly check that out tomorrow and see if anything obvious is bad

Good question @swathdiver got any documentation on the volts/ohms?

 

[Doubeleive]

I have read that before replacing the tccm that a dealer can reprogram it or at least tell you if it's the module that has shit the bed. Is this something a used part would work for? I have a few self service junk yards near me and I could pick one up from them for pretty cheap

I wouldn't worry about the tccm just yet it's more likely to be the encoder motor, if it drives/shifts ok and you just do not have 4wd I would not suspect the tccm

 

[Ialsofkdyourdad]

I wouldn't worry about the tccm just yet it's more likely to be the encoder motor, if it drives/shifts ok and you just do not have 4wd I would not suspect the tccm

Yea it drives perfect. I'll see if everything is connected, I just ordered a scanner so I can use the app scottydogs suggested, should be at my house on Tuesday so if it's not a faulty ground or unplugged harness Ill give it a scan.


I'll look into an encoder motor now but I just bought the truck a week ago so if it's expensive I may have to put fixing 4wd on the backburner