DTC P0502: Vehicle Speed Sensor (VSS) Circuit Low Input
- Test-drive the vehicle.
Is the speedometer indication correct?
YES – Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the VSS and at the ECM. 
NO – Go to step 2.
- Check the vehicle speed with the scan tool.
Is the correct speed indicated?
YES – Go to step 3.
NO – Replace the VSS.
- Turn the ignition switch OFF.
- Disconnect the VSS 3P connector.
- Turn the ignition switch ON (II).
- Using a DVM to battery +, probe the connector ground wire (terminal No. 2).
Wire side of female terminals
Is there B+?
YES – Go to step 8.
NO – Repair open in the ground wire.
- Measure at the VSS connector between voltage supply (terminal No. 1) and ground (terminal No. 2).
Is there about B+?
YES – Go to step 9.
NO – Repair open or short to ground which may have a blown meter fuse.
- Measure at the VSS connector between ground and the wire from the speedometer.
Is there about 11 – 13 V? (At peak voltage.)
YES – Repair open or short circuit between the speedometer and the VSS.
NO – Replace the speedometer.
- Check at the ECM connector between No. A49 terminal and the wire from the speedometer.
Was a problem found?
YES – Repair open or short circuit between the speedometer and the ECM.
NO – Go to step 10.
- Test-drive the vehicle.
Is the speedometer indication correct?
YES – System OK.
NO – Substitute a known-good ECM and recheck. If symptom/indication goes away, replace the original ECM.
| NOTICE |
The battery power supply short circuit to 5 V power supply damages the ECM.