I have been having a problem with my blazers 4x4 fora while now, hopener it's starting to become a nuisance. The blazer is a 99 with the 3 button 4wd and it will shift in and out of four wheel fine but only three or four times. After that I have to unplug the pattern and let it drain out and then four wheel works fine again. After it stops letting my shift in and out of four wheel when I hit the button the orange light for whatever I'm switching lights up briefly and the text clicks but nothing else happens. After resetting battery it will shift in and out pretty quickly without any problem

Also, if I do need a tccm am I only able to get the ones with my same part number? Or will any tccm from a 98+ with three button 4wd work?

Just looking to see if anyone else has had this problem and what their experience was. I have replaced the switch and I got the same results

 

Sounds like a "dirty" encoder. Wife's '04 did the same thing. After a few shifts the TCCM would go into "fail soft" and only shift from 2-Hi to 4 Low..


Originally Posted by Fred Nutcase
Encoder repair on Wife's '04 Blazer.... pictures at: www.rlfarms.com/blazer/

Blazer's 4x4 has been flakey for several years, but on the ranch in central California it never snows so, 2-hi and 4-low worked fine.... But we moved to Reno, Nv. and winter is comming (it snowed a few days ago at Lake Tahoe, so it's comming here in a couple of months). Reading through the GM shop manual, only 2-hi and 4-low IS a FAILURE mode the TCCM (transfer case control module) goes into when it can't properly "read" the encoder signals. To see DTCs (diagnostic for the 4x4 system, ground pin 13 of the ALDL (assembly line data link) connector (under the dash near the steering column), turn ignition key to "on", observe the DTCs on the 4x4 push button's LEDs. Hers had a DTC of 002 (bad encoder or connections). I've cleared the codes before (by unplugging the TCCM for a while so the capacitors could discharge) and it would shift fine for several shifts, then revert to only 2-hi and 4-low again. So, time to fix it (before it snows). I unplugged the connector from the encoder/motor and checked the "channels" with a voltmeter (turn ign key to "on" and measure the channel pins to ground, should be 5.0 volts +/- 0.4) OK. I removed the Encoder / Motor assembly (after removing the front driveshaft), and took the unit into the operating room (aka the kitchen table). I removed the three security torx screws and seperated the encoder from the motor / gear assembly. SEALED.....DANG.... so I tested the Encoder "switch" for channel "A"... WOW, while SLOWLY rotating the encoder, the ohmmeter jumped from 0.9 ohms to 40.0 ohms to 300.0 ohms (very flakey), then open, then back to ground at the other end of travel. I figured if one channel is bad, odds are the other channels are bad too. Well, it's only core value now, so nothing ventured....... I took my pin vise with a SMALL drill bit and drilled two SMALL holes just on the inside of the "O" ring (see web pics). Introduced some contact into the switch assembly with a syringe (the wife is a nurse, she gives me some very handy tools!!!). I rotated the encoder "switch" through its range of travel several times (like 30) and retested the "channel" pins to the ground pin. Very low resistance and steady, either ground or open for A, B and C, depending upon position, no more high resistance. Channel P is a "pulse" to ground while the encoder is rotating. Reattached the encoder to the motor assembly and reinstalled it into the truck. Cleared the DTC by unplugging the TCCM for several minutes. Tested the truck on and offroad, shifted just fine!!!! many many times... FIXED, at least for now... Later I thought that I should have put a drop of silicone seal or black tape over the holes....... oh well.....