Output Speed Sensor Circuit (1991 - 2WD "C" & "K" Series): Notes

Fig 1: Output Speed Sensor Circuit Diagram (1991 - 2WD "C" & "K" Series)

Courtesy of GENERAL MOTORS CORP.

The speed sensor, which is a Permanent Magnet (PM) generator, provides Digital Ratio Adapter Control (DRAC) with vehicle speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever vehicle speed is more than 3 MPH. Voltage level and pulse increase with vehicle speed. DRAC converts this signal to a pulsing signal by grounding circuit 437 (Brown wire) 2000 times per mile. Control module uses this signal in calculations to determine vehicle adjustments.

1. This step tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step checks if vehicle speed sensor signal is present at DRAC.
3. This step checks output speed sensor signal.