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 trouble codes) 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 cleaner 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.....
