P0503
DTC P0503
Circuit Description
Vehicle speed information is provided to the engine control module (ECM) by the vehicle speed sensor (VSS). The VSS is a permanent magnet generator that is mounted on the transmission and produces a pulsing voltage. The AC voltage amplitude and frequency increases with vehicle speed. The ECM converts the pulsing voltage into km/h (mph). The ECM supplies the necessary signal to the instrument panel for speedometer, odometer operation and to the cruise control module. The ECM also supplies the signal to the body control module (BCM), and the electronic suspension control module, if equipped.
If the ECM detects a vehicle speed drop for 6 seconds, DTC P0503 sets. DTC P0503 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0503 Vehicle Speed Sensor (VSS) Circuit Intermittent
Conditions for Running the DTC
* No MAP sensor DTC P0106.
* No idle control system DTCs P0506 or P0507.
* No TP sensor DTCs P0120 or P0220.
* The vehicle speed is greater than 13 km/h (8 mph) for 6 seconds and has not increased by 6 km/h (4 mph) or greater for at least 0.5 seconds.
* All conditions are met for more than 6 seconds.
Conditions for Setting the DTC
The ECM detects a vehicle speed drop for 6 seconds.
Action Taken When the DTC Sets
* The ECM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
* The ECM disables Cruise Control.
* The ECM commands the coolant fan ON.
* The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records.
* The ECM stores DTC P0503 in ECM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
Conditions for Clearing the MIL/DTC
* The ECM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
* A scan tool can clear the MIL/DTC.
* The ECM clears the DTC from ECM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
* The ECM cancels the DTC default actions when the fault no longer exists and the DTC passes.
Diagnostic Aids
Ensure the VSS is correctly torqued to the transmission housing.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
4. The vehicle speed detector in the ECM and the VSS are matched in such a way that an open or a short to ground in the VSS low signal circuit will not usually cause a loss of speed signal or a DTC P0503 to set.
7. This step isolates the short between the VSS and the wiring.
9. The DMM will detect AC voltage if the VSS high signal circuit is shorted to ground.
Step 1 - Step 6:
Step 7 - Step 14:
