Speedometer inoperative; TCM code 232

[dusteddisgusted]

Hi guys,

I have a 1992 960 with 78k miles. The speedometer does not register anything, and the TCM is showing a fault by flashing the up arrow on the instrument cluster and flashing the sport/economy mode switch. I performed the self check using the diagnostic port in the engine compartment and pulled a code 232 - speedometer signal missing. The vehicle speed sensor on the rear of the differential has already been replaced. Although I have not found any reference material describing the operation of this circuit, I believe the vss feeds to the ABS module. There is a take off of the vss signal (one wire) that goes to the instrument cluster, which then either modifies or passes along the signal to the TCM. I finally found a schematic and verified the circuit integrity of the vss circuit ( wht/grn and wht/brn) to the ABS module (I am aware that the ABS module is not multiplexed on this vehicle). According to the schematic I have, the wht/grn wire is spliced and goes off to the cluster. This circuit tested good at pin D3 of the instrument cluster. I also verified what I believe is the vss signal wire from the instrument cluster to the TCM (grn/blk from pin A3 of the i/c to pin B8 of the TCM). All circuits have 0 ohms of resistance. I am at the point of condemning the i/c / speedometer, but wanted to verify both the signal to the i/c as well as the signal to the TCM. I'm confident that the vss will read out in a/c voltage, as it looks like a two wire vrs sensor with no logic gate. I am unsure, however, as to what signal the i/c sends to the TCM. Processors prefer a digital signal. I was hoping you guys could a) review my logic in condemning the i/c / speedo and my inference of the operation of this system, and b) tell me what type of signal is being sent to the TCM by the i/c and give me reference values so I can verify the signal is missing/corrupted/out of spec.

Thanks for any help in advance.