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a little 4wd info
The encoder motors commonly fail on the 2002+ autrotrac (4 4wb buttons) blazers and s10 p/u's. A printed circuit board contact "cooks out" inside the encoder motor confimation switches. Just so you know, the A,B, and C switches tell the TCCM what general shift postion they're in. the P switch is a singal to the TCCM when to stop the motor (final park postion). I am pretty sure A is 2wd, B is 4wd hi, and C is 4wd low. If you're a little clever w/ electronics, you can also fix the TCCM problems w/ new relays. I totally ditched all the "electronic control" for the unit. Since I never use 4wd hi, I just manually operate the electric motor all the way when switching modes. Just back the motor up a tick to prevent the excessive shift fork wear. The vac operated front diff used to be operated by powering it w/ a switch. I removed the collar setup on my ZR2 by putting in a old bravada passenger axle stub. This eliminates the sldiing collar all together and makes it a full time front axle. I offroad with my truck and only drive it to spots, so this may be rather different than most people here.
Thanks for this blog! My
Thanks for this blog! My problem was would shift into 2hi and 4hi no 4lo Cleaned the corroded pins works perfect! Thanks agian.
15741322 transfer case control module problems
I really wish I found your blog before I replaced my tccm. I live in Canada and my 4wd stopped working. I have a 2003 blazer and where I live 4wd is an absolute must. I took it to a shop and they could not figure out the problem, so then I took it to the dreaded dealer. They gave me a quote of $1800.00 to replace my encoder motor and transfer case control module. I certainly could not afford this so I took the estimate and found the parts on ebay, then I took it to the first shop and paid them $200 to install everything. I picked up the truck and everything worked great. I wish I had thought to check the connectors as if that was the only problem, then I could of saved a ton of money and probably could have gone on a week vacation. Anyway gotta love eBay, I got the tccm for $300(dealer wanted $550)and the transfer case encoder for $190(dealer wanted $680 for this). Great blog and great work. Thanks for posting
Front Wheel Drive Actuator
I found on my 1999 GMC Jimmy the best way to check to see if the actuator under the battery was working is to simply pop the headlight assembly out. All you need to get it out is to pull up on the two strips locking it in place. There's a hole behind the assembly that gives you a birds eye view of the actuator.
connector
Thank you for your post on the 4 wheel drive relay connector. I didn't find it until after I replaced the in dash switch, the corosion was so small you never would have seen it if you were not looking for it. So thanks again Bill Shoner Whitmore lake Michigan
Problem Solved
Great Blog. I have a 2004 Blazer which would not engauge the 4x4. From all the info posted I was able to gather that my problem was not an electrical one. It turned out to be the vacuum line. It is encased in a plastic wire gathering material from the firewall to the front battery. It runs along the engine and then branches off to under the battery. Right at about the front of the engine the casing and vacum line itself had melted in half. Must have worked its way too close to the exhaust manifod. I inserted a small steel tube to each half of the hose to connect the vacume line. This worked. I now have 4x4.
Best Regards to all,
John
2002 Trailblazer no 4wd
Kyle, seems like you are well versed in identifying and trouble shooting GM's failed AWD system. my problem, no 4wd.. symptoms.. no light at switch, not even the 2wd light. Replaced the switch, no change. No click when the switch is turned to AWD/4H /4L.
Removed the acutator, picked up the 12 little gears that went bouncing across the bay floor and reassembled. Used a scan tool and find that htere is no communication to the transfer case program. The engine codes will scan but no communication to the t/fer case. At this point I suspect the TCCM but can't find it.. any thoughts.. thanks George V