Code 24, Vehicle Speed Sensor - 1992 6.2L Diesel: Notes

Fig 1: Code 24, VSS Circuit Diagram (1992 6.2L Diesel)

Courtesy of GENERAL MOTORS CORP.

ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to vehicle speed sensor (VSS), which alternately grounds circuit No. 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and ECM will calculate vehicle speed based on time between pulses.

Code 24 will set if circuit No. 437 voltage is constant, engine speed is more than 2000 RPM, or vehicle speed signal is less than 5 MPH. All conditions must be met for 40 seconds.

1. This test monitors ECM voltage on circuit No. 437. With wheels turning, pulsing action will result in varying voltage. Variation will be greater at low wheel speeds to an average of 4 to 6 volts at about 20 MPH.
2. A voltage of less than one volt at ECM connector indicates circuit No. 437 wire is shorted to ground. Disconnect circuit No. 437 at vehicle speed sensor. If voltage reads above 10 volts, vehicle speed sensor is faulty. If voltage remains less than 10 volts, circuit No. 437 wire is grounded. If circuit No. 437 is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8 to 12 volts at ECM connector indicates circuit No. 437 is open or a faulty vehicle speed sensor.
4. This is a normal voltage which indicates a possible intermittent condition.