P0502
DTC P0502
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 no vehicle speed for 3 seconds, DTC P0502 sets. DTC P0502 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Voltage
Conditions for Running the DTC
^ No VSS DTC P0503.
^ System voltage is between 10-18 volts.
^ Engine torque is between 40-300 N.m (30-221 lb ft).
^ No TP sensor DTCs P0120 or P0220.
^ The engine speed is between 1,000-6,800 RPM for 8 seconds.
^ The TP angle is greater than or equal to 12 percent.
^ All conditions are met for more than 3 seconds.
Conditions for Setting the DTC
The ECM detects no vehicle speed (0 km/h (0 mph)) for 3 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 P0502 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.
3. This step tests the ability of the VSS to produce an AC voltage. This step also verifies the integrity of the wiring to the ECM.
4. This step tests the VSS circuit for correct resistance.
