justimagination

Just Google, good information. Good luck,
David g.

shifting sequence 99 tahoe push button 4 wd

SWHouston

ok, since you can not get 4hi, then you need to do a code check. Often times an Auto Supply can do this for you free.

Reznut

Got a 2002 Sierra 2500 4 whl. Rear speedo sensor wire at the rear side of trans broke, defaulted to limp mode. Owner thought mechanical trans problem, pulled & I think scammed on repair as truck is still in default 1st gear. I find front & rear speed sensor wires are broken, I repair, re-plugin. Dash 2 to 4 whl touch pad still flashes to to 2whl for a bit then back to 4whl light. Pull the encoder motor, automatic trans fluid is in e-motor gear case, disassemble as this is a used truck & e-motor has been apart from blk silicone, case o-ring gone. Pull the DC motor out of blk plastic case, AT fluid drips out of it. Spray Walmart cheepie brake fluid into end side hole of motor (grn arrow) & blow into hole with compressed air. Have a rag around the motor as AT fluid blows out. I repeated this about 5 times, half a can of Bfluid. Tested motor with battery 12 volts, it works both rotations. I took pics of the position of the selection sensor to transfer case when in the stuck 4Lo position. The selection switch has white silicone around the cover so I pry the cover off. Ahh, no electrical contacts like the good ole days. The sensor uses varying magnetic force to a chip sensor to indicate at what position shift mode of the Tcase. So, ATF in the DC motor might have impeded its operation, no or loss of motor torque. ATF also high probability of impeding proper magnetic force to sensor pickup chip. Cleaned the selection sensor of ATF. This is as far as I am now. Hope this connects some gray areas as it did for me to understand the TCCM in better wise. I am getting the gist that error codes pertaining to the 4 whl circuit have to be cleared for proper actuation of the circuit. But, it takes a specific type of scanner diagnostic tool, GM Tech II, to access the 4 whl auxiliary app to clear the codes then the selection switch has to align to the Tcase in Neutral. Neutral is when the forward driveshaft & main drive shaft spins free with the trans in Park. That is the big test tomorrow. Will ck the TCCM for bad solder cracking possibly needing a touch from a hot solder tip. Good advice was to snag a used cleared TCCM from a salvage yard & install to circumvent the old unit with error codes.

Pic of selection switch before removal



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Angle of swing gear when stuck in 4L




GM or New Process 246 DC encoder motor showing hole to spray cleaning fluid into & blow with compressed air



GM encoder motor selection switch, there is no old type electrical metal to metal contacts