Hi
2000 Blazer 4dr nv236 (2 speed 4 button with auto 4x4).
I am trying to diagnose an issue with my blazer where when I put the tranny into reverse the service 4wd light comes on. The light does not come on in drive or any forward gear and resets when i shut off the key and restart.
I have read through the DIY section, which is very helpful and the schematics were very useful. I've checked switch resistance, cleaned TCCM connections, encoder and motor connections and had codes read by a shop Cleaned tranny connections and checked that reverse switch is working
The code was for a "shift delay" and have no other vehicle codes. Don't know the exact nomenclature but that would coincide with the delay in getting a 4HI indication when i engage the 4x4. It does work and switches back and forth although sometimes a little finicky.
I had the shift assembly out and checked for corrosion or damage and it looked fine and encoder resistance checked out ok in its current position. (something like 8ohms in 2HI).
Front axle works fine, no vacuum leaks, cable is smooth with full travel.
My concern is what would cause the 4WD light to come on when I put the tranny in reverse but not forward. All the while without selecting any 4x4 mode.
So before I purchase a new encoder motor assembly: Is there a relationship between the TCCM circuit and the transmision? i.e. shift positon sensors, vss's, and or the encoder?
And what would cause the service light to come on only in reverse.

 

problem solved. The scanner described problem was with the shift lock solenoid. It turned out to be a wire in the harness that passes through the transmission tunnel to the engine compartment. The tight clearance had rubbed through the insulation and was causing an intermittent ground. When I put in reverse the torque would push the tranny against the wire making it ground out. There should have been a wire jacket covering the wires in this area but a portion was missing. Likely due to negligence during some previous service work.