Except California

Vehicle Speed Sensor Circuit:

To test the Vehicle Speed Sensor (VSS), located in the speedometer, proceed as follows.


COMPONENT TEST
1. Connect an analog voltmeter between ECM pin 18 and ground.

NOTE: To test pins do not remove the connector from the ECM, instead insert a straight pin or needle from the back side of the connector to access the pin.

2. Turn the ignition switch to the "ON" position, without starting the engine.
3. Raise one drive wheel off the ground and manually rotate the wheel slowly.
4. Observe the voltmeter, the voltage should oscillate between approximately 5 and 0 volts, as the wheel is rotated. If this occurs the Vehicle Speed Sensor system is operating properly.
5. If the voltmeter remains steady at 5 volts there is either an open circuit between the VSS and the ECM, or the VSS is faulty. Before replacing the VSS check for an open circuit in the VSS or instrument cluster grounds.
6. If the voltmeter remains steady at 0 volts, there is either no reference voltage from the ECM, a ground between the ECM and the VSS, or the VSS is faulty.
7. To determine if the VSS is grounded or faulty, turn the ignition switch "off" and test for continuity between ECM pin 18 and ground (using the same test method as in step #3). If continuity alternates, the VSS is operating properly (the ECM is faulty). If continuity remains constant, either there is a short between the VSS and the ECM, or the VSS is faulty.

NOTE: There should be continuity and non-continuity 4 times for every rotation of the speedometer shaft.

HARNESS TEST
1. Disconnect the ECM connector. Raise the drive wheels off the ground.

2. Using a Ohmmeter, check the speed sensor output circuit for continuity between the ECM harness connector terminal 18 and ground, with the drive wheels turning.

Continuity:
Should alternate ON and OFF.

3. Reconnect the ECM connector, remove the instrument cluster connector and turn on the ignition. Measure the power supply voltage between instrument harness connector terminal 1 and ground.

Voltage:
4.5 - 4.9 Volts.

4. Check for continuity of the ground circuit, between the instrument cluster harness connector terminal 10 and ground.

Continuity:
Should exist.



If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, clear the trouble codes and road test the vehicle to confirm that the repair has corrected the problem and the code doesn't return.


If the same trouble code reoccurs, it is possible that there is an intermittent failure of the component or the ECM. Check for looseness at all harness junctions and test for an intermittent failure.