Check the Neutral/Brake Safety switch, if you read Chevy Lovers post if that switch is malfunctioning it could affect the TCCM...reread the post...

 

Get a new TCCM. I had to a year ago. (we have the 4 button 4wd too.)

The problems you have sound familiar.

 

Well,I figured out what my problem THIS TIME was! I mean that I am quite sure that I will have more trouble with this vehicle. I wish my wife didn't like it so much.

As I stated before, the ATC fuse blew and I replaced it. The Service 4 WD light was on and no lights were lit on the dash switch. I took it to a buddy's place to connect it to a code reader. He has a Snap On MT 2500 and we tried to capture a code. There was none, but the Service 4 wd light was still on(not sure if maybe he needs some more experience using the unit). My buddy has a vehicle lift and he had an idea. It seems that he likes to tap things with a hammer, and told me to get in the truck,put it in drive and he started tapping the transfer case motor and front diff. Would you beleive that when I shut it off(while still on the lift), and then restarted the Blazer, the 2wd light came on the switch!! I put the thing in 4 wd and the 4h light came on for a second and they all went off again. We let the Blazer down and the ATC fuse was blown again. I assumed that somehow he released something in the Transfer Case Encoder Motor and took the thing home. I tried putting a new ATC fuse in but it blew instantly.I got under the truck with a meter and started testing. This is what I figured out: The Encoder motor has 2 plugs. The 4 pin plug is what controls the motor while the six pin plug is the position sensor. On the motor plug there is a thicker red and a thick black wire. When I replaced the ATC fuse the thick red wire from the wiring harness has voltage. The thick red wire going into the motor had a .8 ohm short to ground. Obviously that is what was blowing the fuse. I got a rebuilt encoder motor and tested the red wire and found that there was a 7 ohm short to ground. I assumed that replacing the motor would fix my problem and changed it. Of course the negative battery terminal had to be disconnected for quite awhile to clear the codes, but when I connected everything, it works like new.
I was pretty sure that the trouble was not the TCCM because that thing went about six months ago and I got a replacement. I could not find any after market TCCM suppliers so a new one from GM was about $965 CAD. I found one on Ebay cheap.
I would try replacing the cheaper parts first if you are still trying to fix it yourself. I have been reading alot of forums and it seems that the encoder motor is a very common problem, so I figured that I would need one sooner or later. I found a rebuilt one for $270 CAD and it only takes about an hour to change.
Good luck and sorry for the long post.

 

"the Service 4WD light stays on from initial crank. The control switch (dash) blinks all lights once for just a millisecond, but the normal self check clicking and light patterns are not there."

I've been fighting this problem for about a year now with no real direction. My 4wd selector switch (on the dash) is generally unresponsive and shows no real sign of life. I have, however, seen the brief occasion for the vehicle to start with the "service 4wd" light still on the gauge panel, but with the 2wd light on the selector switch illuminated. Anything I press from there (4HI, 4LO, AUTO) causes the selected mode to blink, and blink...and then time out. Then I get nothing all overagain on the selector switch.

I have an OBDII scanner, but do not have a chassis module...so I cannot read 4wd system codes. I've brought the truck to 3 shops to have codes read...and no one seems interested. Each, seperately, told me not to bother to have codes read because the GM 4wd codes arecryptic at best (ie: 4wd failed to transfer). They seem to believe that old school process of elimination is the only way.

So far, I've been through both relay and fuse boxes (under the dash and under the hood), I've been through the entire vacuum system (that I can get to) and replaced the hoses, I've replaced the selector switch, I'veinspected the vacuum actuator under the battery to be sure that it is free to move and that there are no tears in the diaphram, I've been through all electrical connections (that I can get to) and inspected for wiring damage or corrosion...and nothing has made any difference at all. In all of this, all I ever found wrong was a vacuum hose showing signs of dryrot. That, along with the others, has been replaced.

At this point, and ss far as I can tell, there are 3 components targetable for blind replacement...

There is a solenoid valve at the top of the firewall on the drivers side that seems to direct vacuum to the vacuum actuator (if working properly). There is the vacuum actuator, and there is the transfer case encoder motor. I'm not sure how much the solenoid vlve costs. But, of the other 2 parts, the vacuum actuator is the cheaper. So, I'm thinking of starting there.

These sets of circumstances, described as:

"the Service 4WD light stays on from initial crank. The control switch (dash) blinks all lights once for just a millisecond, but the normal self check clicking and light patterns are not there."

seem to be uniquely seperable from many of the other symptoms of 4wd system failure. Has anyone with these exact symtoms been able to directly correlate the origin of the failure to one of the three components I mentioned (or any other)???

The closest correlationseems to come from the guy who likes to tap on stuff.

Good luck to everyone...I'll be watching.

Icarus

 

OK...

I have more info. I changed my ball joints last weekend, and had an appointment with one of the chain shops for a front end alignment. I got them to read the chassis codes (for free)...and this is what I've got:

Current:

DTC 323: Transfer Case Lock Circuit Low
DTC 308: Motor A/B Circuit Low

History:

DTC 387: Unable to complete shift
DTC 2725: Active Transfer Case Mode Malfunction

Without some help, experience, or documentation, I'm not sure where the codes point me. Transfer case lock circuit low could mean that the transfer case motor isn't engaging the front transfer case linkage due to low voltage...but I don't know. Not sure what the A/B circuit is...etc.

Can someone help point me to probable origins for the DTCs,or to probable origins ofthe problems I'm having (supported by the DTC codes)???

Thanks in advance.

Icarus

 

I think I have more info:

I also learned that the encoder motor has 4 channels. I believe the self test procedure moves through the 4 (P, A, B, and C) channels to simulate transfer through the 4 modes or ranges (auto 4wd, 2HI, 4HI, 4LO).

DTC C0308 seems to mean that the self test failed because there wasn’t sufficient voltage to move the transfer case motor from the channel A position to the channel B position (or vice versa).

Check this out:

http://www.transmissiondigest.com/te...09UpToStds.htm

I think this all points to the transfer case (encoder) motor.

 

I'll check things out more when I get home from work, but that is a great link. None of my references give the detail into the auto transfer case, but then again, I don't have my GM eSI installed anymore... LOL. I'll have to do that again sometime on my workstation downstairs.

 

I have had alot of these trucks come in with 4WD concerns that were caused by a leaking winshield........yes the windshield.....check the big connector on your TCCM to see if there is water intrusion. What happens is the winshield leaks and water runs down theA-pillar down the harness and right in theTCCM connector. You need to check for signs of this. There is usually green death (corrosion) at the module connector.

 

Alright...

Just for giggles, I did jumper DLC pin 13 to ground...and got no stored codes.

Sorry for the stupid question...but where is the TCCM located? I was initailly picturing the ECM in my mind...and that's obviously not what you're reffering to. ECM connectors do look good though.

The vehicle is a 2000 4dr 4wd LS 4.3l V6.

I'd like to check the TCCM connectors, and revisit the connectors at the encoder motor. I want to be sure before I replace the part that the low voltage condition isn't because of a connection somewhere. I had also hear that there is a 3rd fuse / relay panel behind the glove box. I plan to check that out as well.

Thanks,

Icarus

 

The TCCM should be behind the passenger side kick panel directly infront of the front passenger door.

As to why the grounding of pin 13 didn't do anything, that method only works for the non-auto transfercases. The Auto & AWD transfercases use serial communication.