P0502
DTC P0502
Circuit Description
The vehicle speed sensor (VSS) assembly provides vehicle speed information to the engine control module (ECM). The VSS assembly is a permanent magnet generator. The VSS produces alternating current (AC) as the rotor teeth on the output shaft of the transmission, 2WD, or transfer case, 4WD, pass through the magnetic field of the sensor. The frequency and amplitude of the AC waveform increase as vehicle speed increases.
If the ECM detects no vehicle speed for a specified length of time, while other sensors indicate that the vehicle is moving, 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 TP sensor DTCs P0120 or P0121.
* No VSS DTC P0503.
* The TP indicated angle is 8 percent or more.
* The engine speed is 500-6,500 RPM.
* The engine torque is greater than 50 N.m (37 lb ft).
* The system voltage is between 9 and 16 volts.
Conditions for Setting the DTC
The transmission output speed is 52 RPM or less for 4.5 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 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 ignition cycles 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.
