P0502

DTC P0502

Schematic:

Circuit Description
Vehicle speed information is provided to the Powertrain Control Module (PCM) by the Vehicle Speed Sensor (VSS). The VSS is a permanent magnet generator that is mounted in the transaxle. The VSS produces a pulsing voltage whenever vehicle speed is over approximately 5 km/h (3 mph). The AC voltage level and the number of pulses increases with vehicle speed. The PCM converts the pulsing voltage into km/h (mph) and then supplies the necessary signal to the instrument panel for speedometer, odometer operation and to the cruise control module and multi-function alarm module operation.

Conditions for Running the DTC
- Engine speed is 1,700 - 3,600 RPM.
- Throttle Position (TP) is 0-1 percent.
- Engine vacuum is 70 - 80 kPa.
- The above conditions are met for 5 seconds.

Conditions for Setting the DTC
Vehicle speed is less than 3 km/h (2 mph).
Action Taken When the DTC Sets
- The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
- The PCM disables Cruise Control.
- The PCM commands the coolant fan ON.
- The PCM records the operating conditions at the time when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
- The PCM stores P0502 in PCM history.

Conditions for Clearing the MIL/DTC
- The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic runs and passes.
- The PCM cancels the DTC default actions when the fault no longer exists and the DTC passes.
- The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
- A scan tool can clear the MIL/DTC.

Diagnostic Aids
Ensure the VSS is correctly torqued to the transmission housing.

Test Description

Steps 1-6:

Steps 7-14:

The numbers below refer to the step numbers on the diagnostic table.
5. The resistance measurement will not change if either the VSS high signal circuit or the VSS low signal circuit, but not both, is shorted to ground. The vehicle speed detector in the PCM 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 P0502 to set. The lower resistance value given represents the nominal resistance specification of the VSS at -40°C (-40°F), minus the manufacturing tolerance specification of 10 percent. The higher resistance value given represents the nominal resistance specification of the VSS at 150°C (302°F), plus the manufacturing tolerance specification of 10 percent.
8. This step isolates the short between the VSS and the wiring.
10. Do not skip Step 7. The DMM will detect AC voltage if the VSS high signal circuit is shorted to around.
13. The replacement PCM must be programmed and the crankshaft position system variation procedure must be performed.