Upgraded Emissions

CODE 24 VEHICLE SPEED SENSOR (VSS) CIRCUIT

Diagnostic Chart:

VSS Circuit:

CIRCUIT DESCRIPTION
The Vehicle Speed Sensor (VSS) consists of a reed switch built into the speedometer head. The Engine Control Module (ECM) provides 5 volts to the VSS. As the speedometer cable turns, the reed switch closes the circuit to ground four times per revolution of the speedometer cable. As vehicle speed increases, the frequency of ground pulses received by the ECM also increases. Therefore, by calculating the frequency of the ground pulses, the ECM is capable of determining vehicle speed.

Diagnostic Trouble Code (DTC) 24 will set if the following condition is met for at least 4 seconds: A constant voltage signal (either high or low) detected at the ECM with the engine running and the vehicle moving.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Checks to see if problem is intermittent.
2. If the VSS is not receiving the 5 volts from the ECM, DTC 24 will set. This step checks for an open in the YEL/GRN wire or a faulty ECM.
3. This checks for a poor ground connection, an open in the BLK/BLU wire or for a faulty VSS.

DIAGNOSTIC AIDS
If the speedometer cable is binding, DTC 24 can be set. Make sure that the speedometer cable is free from any restrictions and that it has a secure connection to the Instrument Panel (I/P) cluster assembly.

Refer to Diagnosis By Symptom / Intermittents. - Intermittent Malfunctions