Input Speed Sensor Circuit Check: Notes

WARNING: This page does not describe the selected car, but rather 23 other vehicles, including the 1991 GMC Vandura Special, 1991 GMC Vandura, 1991 GMC Value Van, 1991 GMC Suburban, and 1991 GMC Rally Camper Special. However, it is still accessible from the selected car via links, so may be relevant.

The input sensor is of the magnetic induction type and is located on the left side of the transmission, forward of center. Serrations in the forward clutch housing induce a small A/C current as they pass by the input sensor. While there is no specific code for an input sensor problem, the PCM/TCM uses input sensor readings to calculate gear ratio, turbine speed, TCC slip, and determine if the engine is running.

NOTE: Test numbers refer to test numbers on diagnostic chart.

This test checks the input sensor circuit up to the PCM/TCM.
This test checks the sensor output.