4WD Inop
- Thread starter darceye
- Start date
Just an FYI... when my TCCM went south, I didn't get a 4 Wheel drive light. The indications on the switch would flash on turning the key (and so did the 4 wheel drive light) and then go dead. When I pulled the #8 fuse, it was then I got the 4 Wheel drive light which remained on then until I replaced the TCCM. I noticed several have posted they didn't get the 4 wheel light but lost the switch lights... that seems to be one path for all of this.
Bitz
Bitz
After traveling down the highway in heavy heavy rain my service 4WD light illuminated. I was unable to switch into AWD,4 hi or 4 low. It sounded like the front axle actuator was working, as was the encoder motor. So I thought.
Found fuse 48 blown. Hmmm. Didn't really find anything so I replaced the fuse. All was working fine until later the next day when traveling in rain again, the service 4WD light comes on again, fuse blown again. Long story short, I found an intermittent short to ground on the brn wire going from C3 E4 to the suspension control air compressor. It was about six inches back from connector. The brown wire was pushed out of the loom and chaffing on the frame.
Go figure
Found fuse 48 blown. Hmmm. Didn't really find anything so I replaced the fuse. All was working fine until later the next day when traveling in rain again, the service 4WD light comes on again, fuse blown again. Long story short, I found an intermittent short to ground on the brn wire going from C3 E4 to the suspension control air compressor. It was about six inches back from connector. The brown wire was pushed out of the loom and chaffing on the frame.
Go figure
Andy0x1
Member
- May 26, 2013
- 3
Resurrecting an old thread here.
I have an 02 Envoy SLT w/just over 200K miles.
I've only owned it for ~500 of those miles.
I bought it cheap, with a TON of problems.
No Dash lights -> Moved switch from 2H to 4H, and it made a click sound, the lights dimmed, and the Service 4WD light came on.
At this time, the batt was bad, I figured the alternator couldn't handle the momentary current spike, and that's all it was.
After installing a new battery, the light remained lit.
I pulled the #8 fuse. I disconnected the battery, nothing I did would reset it.
I drove ~10 miles, made a stop, and when I got back to the vehicle the light was out.
I tried flipping the switch the 4H, and it worked fine.
For the next few weeks the 4WD was fine.
Then it happened again... Switching to 4H made the light come back on.
I ordered an 03 TCCM from someone on eBay.
Installed it, still have the light.
I bought some Track II fluid, did the change, the old fluid looked new. I noticed RTV silicone around the transfer case so I'm thinking the entire thing may have been serviced in the past?
I've switched back and forth between the 02, and 03 TCCM's with no change in symptoms.
At Key on, the range selector will illuminate all positions for 2 seconds then go dark.
Holding it past 4L (N?) with key off, or on, doesn't help, nor does pulling fuses, or the battery.
What are causes for the 4WD light to illuminate? I question if I was sold a bad TCCM as I would have expected there to be no light until an attempt to engage 4H was made.
I have a meter, and can check wires if need be, I wish I knew someone with a known good Module I could try since it's so easy to get to.
I have an 02 Envoy SLT w/just over 200K miles.
I've only owned it for ~500 of those miles.
I bought it cheap, with a TON of problems.
No Dash lights -> Moved switch from 2H to 4H, and it made a click sound, the lights dimmed, and the Service 4WD light came on.
At this time, the batt was bad, I figured the alternator couldn't handle the momentary current spike, and that's all it was.
After installing a new battery, the light remained lit.
I pulled the #8 fuse. I disconnected the battery, nothing I did would reset it.
I drove ~10 miles, made a stop, and when I got back to the vehicle the light was out.
I tried flipping the switch the 4H, and it worked fine.
For the next few weeks the 4WD was fine.
Then it happened again... Switching to 4H made the light come back on.
I ordered an 03 TCCM from someone on eBay.
Installed it, still have the light.
I bought some Track II fluid, did the change, the old fluid looked new. I noticed RTV silicone around the transfer case so I'm thinking the entire thing may have been serviced in the past?
I've switched back and forth between the 02, and 03 TCCM's with no change in symptoms.
At Key on, the range selector will illuminate all positions for 2 seconds then go dark.
Holding it past 4L (N?) with key off, or on, doesn't help, nor does pulling fuses, or the battery.
What are causes for the 4WD light to illuminate? I question if I was sold a bad TCCM as I would have expected there to be no light until an attempt to engage 4H was made.
I have a meter, and can check wires if need be, I wish I knew someone with a known good Module I could try since it's so easy to get to.
TangoBravo
Member
- Dec 5, 2011
- 208
When you select 4hi do you hear both noises? You should hear two different noises if you do not, then search. There are tons of write ups on why you are having the problem you're having and how to fix it.
The typical reason for the dash light to come on is if the PCM can't communicate with the TCCM, and that's usually (but not always) what happens with the bad 2002 TCCMs. But if the TCCM isn't happy with the position feedback sensors of the front axle actuator or the encoder motor, it can also light the dash light. And it should also flash the mode switch light of the mode you're trying to go INTO if it wont' go into that mode.
I agree. You can tell almost anything by listening to the noises. The front axle actuator is a high pitched whine that ONLY happens on 2HI->A4WD transitions and vice versa. The lower pitched encoder motor makes a noise on EVERY mode transition. Check out the noises and the bahavior of the mode switch lights on each transition and let us know.
I agree. You can tell almost anything by listening to the noises. The front axle actuator is a high pitched whine that ONLY happens on 2HI->A4WD transitions and vice versa. The lower pitched encoder motor makes a noise on EVERY mode transition. Check out the noises and the bahavior of the mode switch lights on each transition and let us know.
Andy0x1
Member
- May 26, 2013
- 3
There are no sounds, nor is there any light activity other than the two seconds of illumination at key on. After that the range selector goes dark and stays that way.
The only sound that is heard, is that of the fuel prime pump, and the rattily sound of the electronic gauge clusters.
When the Service 4WD light is 'tripped'. Is it the TCCM module that trips, or is it the Vehicle's PCM?
The Two times the Service 4WD light have come on in the past have always been when moving the range selector from 2H to anything else.
The One time the Service 4WD light went back out was just random after driving to pickup a pizza.
I bought the Envoy specifically to haul my boat, and don't really drive it much at all. I'm nervous about the 4WD not working and getting stuck at a boat launch.
The only sound that is heard, is that of the fuel prime pump, and the rattily sound of the electronic gauge clusters.
When the Service 4WD light is 'tripped'. Is it the TCCM module that trips, or is it the Vehicle's PCM?
The Two times the Service 4WD light have come on in the past have always been when moving the range selector from 2H to anything else.
The One time the Service 4WD light went back out was just random after driving to pickup a pizza.
I bought the Envoy specifically to haul my boat, and don't really drive it much at all. I'm nervous about the 4WD not working and getting stuck at a boat launch.
The PCM runs the dash lamp, and the TCCM runs the mode switch lights.
If you have NO sounds from either of the two motors, you may have other wiring issues. Have you downloaded the schematics and service manuals, and have some electrical troubleshooting experience?
If you have NO sounds from either of the two motors, you may have other wiring issues. Have you downloaded the schematics and service manuals, and have some electrical troubleshooting experience?
Andy0x1
Member
- May 26, 2013
- 3
the roadie said:
I have "HP Tuners" and have programmed cars with it, I see the Envoy is supported, and I've actually attached it to the OBDII port but it doesn't appear to access that portion of the PCM, and no diagnostic codes show up.
I have not checked any schematics. I do have a Beckman multimeter and appropriate experience.
Could a faulty switch illuminate the dash lamp?
I know the climate control dials were kinda sketchy. If you rotated the temperature knob, the set temp would go erratically up / down from bad contacts... Sometimes I wonder if this was a flood vehicle
Is there anywhere specific you suggest I start?
I can do a write up and post pictures for others if it leads anywhere.
Thanks,
-Andy
The TCCM will notice an erratic connection to the switch (because it's an analog resistance choice kind of switch, not a discrete wire selection type), but I'm not certain that error will light the dash lamp.
I would check power and control voltage at the two motors first. And the various pins at the TCCM connector.
I would check power and control voltage at the two motors first. And the various pins at the TCCM connector.
the roadie said:
Having some difficulty nailing down my issue. Hope I can get some advice here:
02 Trailblazer LTZ 135K miles.
Noticed indicator lights on selector switch were not showing at all and no shifting sounds from under the car..silence.
Pulled underhood fuse #8 for thirty seconds and reinstalled.
Restarted vehicle, all switch lights came on for two seconds then went out.
Service 4wd dash light illuminated.
Now, when starting, lights come on for two seconds then go out and service 4wd indicator remains illuminated.
What I've tried:
Replaced tccm with one believed to be ok. No lights at all on selector switch - not even at initial ignition but service 4wd indicator NOT illuminated.
Pulled underhood fuse #8 for 30 seconds: No effect
Put old tccm back in and suddenly every thing worked . ONCE! Now back to original issue.
Voltage at tccm appears to be present. I have a meter and willing to check deeper into this if I can get an idea of what to look for. I have schematics posted by The Roadie. Anything specific I should look for? Ignition on while testing? tccm attached while testing?
Encodor motor??? Selector switch??
Welcome! Glad you found us! As you've probably read, this is the classic symptom of a bad early version TCCM.toytooii said:
The lamp test is a definitive check of a live TCCM. I thought the Service 4WD dash lamp would light up if the lamp test failed, but you obtained a dud TCCM IMHO. Where did you get it, and are you sure it's not another 2002, or from an AWD vehicle like the Bravada that runs the encoder motor but doesn't have the mode control switch? GOt any local buddies you can swap TCCMs with?
the roadie said:
Thanks for reply. Unfortunately, no one else around here with whom I can switch tccm to test.
I've also been thinking the replacement tccm could be a dud and the vendor will fully refund if I send it back to him. It's from a 2005 Isuzu Ascender. I have the VIN for the source vehicle if anyone can check to see what type of 4x4 system it had.
5GADT13S442345507
the roadie said:
I can get a tccm pulled from an '03 Envoy for $40. Assuming that should be compatible???
Ascender has the true 4WD system with the switch and low range. It should be compatible. Bravada is not. Envoy is fine. I have one of those, and I don't go my kind of places without a working low range.toytooii said:
the roadie said:Ascender has the true 4WD system with the switch and low range. It should be compatible. Bravada is not. Envoy is fine. I have one of those, and I don't go my kind of places without a working low range.
NICE!
Thanks for replies. I'll post resolution when it's fixed.
the roadie said:
Roadie,
If I turn the selector switch from 2W/Hi to another position before starting the car, the light on the selected position blinks once and I can hear the motor (not sure if one or both) under the car change to 4 wheel when I sart the engine. I even tried this in 4w/lo and could hear the motor but when I put it in gear, it didn't feel like it was actually in 4w/Lo. Also, although I hear the motors operating, the light on the selector switch does not remain lit for the selected position. Any additional thoughts or does this still lead you to believe it's likely the TCCM? I'll be changing that out next week but wondering if this observation leads you anywhere beyond the TCCM. Thanks for all the help!
the roadie said:Ascender has the true 4WD system with the switch and low range. It should be compatible. Bravada is not. Envoy is fine. I have one of those, and I don't go my kind of places without a working low range.
Replaced TCCM with one from an '03 Envoy. Everything went immediately back to 100% operational. THANKS FOR THE HELP! MOST APPRECIATED!!!