Powertrain Controls - ECM/PCM

DTC 24:

VSS Circuit:

CIRCUIT DESCRIPTION:
The ECM provides a 12 volt signal to the Vehicle Speed Sensor. While the vehicle is moving, the reed switch within the VSS will open and close four times per each revolution of the speedometer cable. Because the reed switch opens and closes, the voltage at the ECM is toggled high and low. The ECM then converts this toggled high/low voltage into a vehicle speed that is displayed in kPh and mph. 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 12 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 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 I/P cluster assembly.