With Automatic Transmission

ALLISON AUTOMATIC TRANSMISSION

DTC P0500 (6.6L)





Circuit Description for Allison Automatic Transmission
The vehicle speed sensor (VSS) monitors the rotation speed of the transmission output shaft. The VSS assembly is a permanent magnet generator. It produces an AC voltage 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 AC voltage frequency and amplitude increase as the vehicle speed increases. The transmission control module (TCM) will send a controlled duty cycle voltage to the engine control module (ECM) that operates in a range of -4.5 volts or +5.0 volts. The ECM converts this signal into vehicle speed. As vehicle speed increases, the frequency of the duty cycle will increase.

DTC P0500 is a type B DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0500 Vehicle Speed Sensor (VSS) Circuit

Conditions for Running the DTC
The engine is running.

Conditions for Setting the DTC
If the ECM detects a difference in vehicle speed with the VSS of greater than 8 km/h (5 mph), then DTC P0500 is set.

Action Taken When the DTC Sets
^ The ECM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs.
^ 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 P0500 in ECM history.

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 ignition switch is OFF long enough in order to power down the ECM.

Test Description








The numbers below refer to the step numbers on the diagnostic table.
4. This step tests the TCM and circuit 400 for voltage at the ECM connector.
5. This step tests for continuity and a short to ground in the wiring system between the TCM and ECM.