Code 24: Vehicle Speed Sensor (Except 3.1L): Notes

ECM applies and monitors a 12-volt signal on circuit No. 437 to Vehicle Speed Sensor (VSS). VSS alternately grounds and opens circuit No. 437 when wheels are turning. This pulsing action takes place about 2000 times per mile. The voltage level and pulses increase with vehicle speed. The ECM converts the pulsing voltage to MPH. The ECM uses VSS information in calculations to determine vehicle adjustments.

A Code 24 sets when MPH is less than 2 MPH, transmission is not in Park or Neutral, engine speed is greater than 1400 RPM, circuit No. 437 voltage is constant and all of these conditions are met for 10 seconds. These conditions are met during a road load deceleration. The 2.8L may set this code while accelerating or at highway speeds.

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

Test Number 1) Monitors ECM voltage on VSS circuit. With wheels turning, pulsing action will result in a varying voltage. Variation will be greater at low speeds to an average of 4-6 volts are about 20 MPH.

Test Number 2) A voltage of less than one volt at ECM connector indicates circuit No. 437 wire is shorted to ground. Disconnect vehicle speed sensor connector. If voltage is now greater than 10 volts, vehicle speed sensor is faulty. If voltage remains less than 10 volts, circuit is grounded. If circuit is not grounded, check for faulty ECM connector or ECM. Before replacing the ECM, PROM should be checked for correct application.

Test Number 3) A steady 8-12 volts at ECM connector indicates VSS circuit is open or speed sensor is faulty.

Test Number 4) This is normal voltage which indicates a possible intermittent condition.