## Diesel Engine Management System

#### DTC Troubleshooting (cont'd)

11-76

DTC P0503: Vehicle Speed Sensor (VSS) Signal Above Upper Limit

1. 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.

1. Check the vehicle speed with the scan tool.

Is the correct speed indicated?

YES – Go to step 3.

NO – Replace the VSS.

1. Turn the ignition switch OFF.

1. Disconnect the VSS 3P connector.

1. Turn the ignition switch ON (II).

1. 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.

1. 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.

1. 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.

1. 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.

1. 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.

a a a