Seeking help with 4wd Issue

N

NebraskaHockey

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Joined
Feb 28, 2014
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Looking for suggestions on a problem with the 4wd on my 2002 Chevy Trailblazer. The 4wd light is on and the selector switch will light up upon starting then goes dark. Tried the fuse trick and unhooking the battery with no change. Got a used TCCM from a 2005 Trailblazer after reading some of the other posts and nothing changed. Also got a new 4wd selector switch from the parts store and that didn't change anything.

Went to a repair shop today to get the codes read and they are C0327 (encoder circuit malfunction) and B2725 (mode switch circuit malfunction). The guy at the shop thought it might be the encoder motor. But from what I've read from other posts, if my lights on the 4wd switch don't light up then my TCCM is still not working?


Has anyone had issues like this? What was your solution? I've read as many other threads on this issue, just not sure what I should be doing next.

Thanks,
 
Welcome! I can't confirm it until I do some experiments someday on a working system, but bad wiring to the encoder motor or to the switch can give failure symptoms like that. What I'm not sure of is if the switch lights will go dark on a failed initial diagnostic of the encoder motor or switch circuits.

Let me consult the shop manual a bit more. We're in the middle of a torrential storm this weekend, so doing the experiments on my vehicle will be tough.

You should leave the newer TCCM installed anyway, since 2002 units were ticking time bombs.
 
The service 4x4 light comes on as soon as you start the vehicle?

If you would like to give testing continuity a go with a multimeter, let me know and I can help you figure out which pins are going to what on different parts.
 
So I wanted to provide an update to the situation and see if it spurs any further ideas. Yes the service 4wd comes on as soon as you start the vehicle. However, yesterday for the first time in the past week the service 4wd went off, however, the four wheel drive selector switch was on 2hi, but the orange light was above 4hi and the four wheel drive was engaged. So I waited till I got back home and tried moving the switch from the 2hi position to 4 hi, it started to blink then the service 4wd light came on and the switch turned off. To help rule out the TCCM I bought a Dorman remanufactured one (said it didn't need to be programmed), but that didn't change anything. I'm think my next move might be to replace the encoder motor, looks like it is pretty easy to access and just four bolts.

If anyone has any other ideas on what could create this problem please share.
 
NebraskaHockey said:
So I wanted to provide an update to the situation and see if it spurs any further ideas. Yes the service 4wd comes on as soon as you start the vehicle. However, yesterday for the first time in the past week the service 4wd went off, however, the four wheel drive selector switch was on 2hi, but the orange light was above 4hi and the four wheel drive was engaged. So I waited till I got back home and tried moving the switch from the 2hi position to 4 hi, it started to blink then the service 4wd light came on and the switch turned off. To help rule out the TCCM I bought a Dorman remanufactured one (said it didn't need to be programmed), but that didn't change anything. I'm think my next move might be to replace the encoder motor, looks like it is pretty easy to access and just four bolts.

If anyone has any other ideas on what could create this problem please share.
Click to expand...

I'm not sure if the encoder and other components actuated by the TCCM get tested on start-up, or only when movement is commanded. I'm kind of wondering if it isn't a wiring issue - like the serial data line leading to the TCCM. Cutting off communication from the PCM would throw an immediate flag, but if the TCCM itself is still in good working order it may still operate, though it may mess up.

My suggestion is to check ALL wiring. I mean ALLLLL wiring, as much as you can access. Especially to the encoder, since it's open to the elements. If it turns out being a wire issue, it's a 10-cent fix instead of hundreds of dollars.

Also, monitor this thread: http://gmtnation.com/f79/4x4-issue-havent-seen-other-threads-9733/#post216539 It's a guy who had the same two codes show up as you.
 
Thanks IllogicTC, I've reached out to him via private message. Wanted to give another update to see if it spurs any additional ideas or insight. So driving home today from work the service 4wd light was on, but the orange indicator light was on above 2hi, whereas usually that has been off. So I tried moving the selector switch and the light would move from 2hi. So I turned off the car, turned it back on and the service 4wd light was off, was able to cycle the transfer case to Auto4wd and 4Hi. Then turned off the car (went inside grocery store). When I came back out the car was in 4hi, no service 4wd light and everything seemed to be working fine. When I got home, I tried to put if back into 2hi, but the orange light above 4hi just kept blinking wouldn't move. So I parked the car in the garage, pulled the #8 fuse, and after 10 minutes but it back in and was able to cycle the transfer case back to 2HI. So took another drive recently, was able to cycle the transfer case while driving from 2HI to Auto4wd to 4HI and back to 2HI again. One thing I did notice is that the car was really jerky while turning, more so that I remember.

Sorry for the long post, hopefully these symptoms will help with ideas of the culprit.

Thanks everyone for the help!
 
I jacked the vehicle up and traced all the wiring from the transfer case. I didn't see anything obvious or blatant. I reseated all the connectors for good measure and took of the encoder motor just for the fun of it. Unfortunately none of it made a difference. I'm gonna TRY to get it in to a recommended shop this week and get a second opinion. I'll update if/when that happens.
 
Hi Guys,
I kind of have the same issue. 2WD AWD 4WDH all work flawlessly and playing in the snow this week I was able to confirm that AWD and 4WDHI are engaging (wheels spinning and throwing snow when the wheels are cut left to right:OP) however when I select 4WDL the light flashes for a few seconds and goes out. Even though the switch is pointing to 4WDL the light for 4WDH stays lit. Any suggestions? Could the TCCM be on it's way out?
 
0u812 said:
Hi Guys,
I kind of have the same issue. 2WD AWD 4WDH all work flawlessly and playing in the snow this week I was able to confirm that AWD and 4WDHI are engaging (wheels spinning and throwing snow when the wheels are cut left to right:OP) however when I select 4WDL the light flashes for a few seconds and goes out. Even though the switch is pointing to 4WDL the light for 4WDH stays lit. Any suggestions? Could the TCCM be on it's way out?
Click to expand...

To get in 4LO, you have to be basically stopped (or going less than 3 mph) and the tranny has to be in neutral. Those are interlocks to keep from destroying the 4WD system by shifting at too high a speed. The procedure is detailed in the Owner's Manual.

ETA: Beat by the master, but I'll leave it.
 
C-ya said:
To get in 4LO, you have to be basically stopped (or going less than 3 mph) and the tranny has to be in neutral. Those are interlocks to keep from destroying the 4WD system by shifting at too high a speed. The procedure is detailed in the Owner's Manual.

ETA: Beat by the master, but I'll leave it.
Click to expand...

Yeah he is defiantly the master and quick!!! I had tried stopped, park, rolled ahead a little stopped then parked again... (never tried it with it rolling as it just seemed like such a bad idea to me) did not try neutral:crazy: I will try that today and let you guys know.

Thanks again
 
0u812 said:
Yeah he is defiantly the master and quick!!! I had tried stopped, park, rolled ahead a little stopped then parked again... (never tried it with it rolling as it just seemed like such a bad idea to me) did not try neutral:crazy: I will try that today and let you guys know.

Thanks again
Click to expand...

Oh and of course he was right.. well both of you were right. (guess I need to find a manual for this thing) Thanks again:smile:
 
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