P0503

Vehicle Speed Sensor (VSS) Circuit:

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 transmission and produces a pulsing voltage whenever vehicle speed is greater than 3 mph (5 km/h). The AC voltage level and the number of pulses increases with vehicle speed. The PCM then supplies the signal to the instrument panel for speedometer and odometer.

Conditions for Setting the DTC
- The vehicle speed is less than 2 mph
- The engine speed is between 1700 and 3600 RPM
- The Throttle Position (TP) is between 0% and 1%
- The manifold absolute pressure is greater than 72 kPa or less than 80 kPa
- The above conditions are met for greater than 5 seconds
- One or more of the following DTCs are not set P0107, P0108, P0122, P0123

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn "OFF" after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- DTCs can be cleared by using a scan tool.

Diagnostic Aids
- A scan tool should indicate a vehicle speed whenever the drive wheel are turning greater than 3 mph (5 km/h). A DTC P0502 can be falsely set if the engine is "braked-torqued" in gear. Disregard if set while the drive wheels are not turning.
- An "intermittent" problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.
- VSS high and low circuits should be thoroughly checked for backed out terminals, broken locks, and for proper routing.
- Refer to Intermittents.

DTC P0503 - Vehicle Speed Sensor (VSS) Circuit Low Input (1 Of 2):

DTC P0503 - Vehicle Speed Sensor (VSS) Circuit Low Input (2 Of 2):

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.
2. The permanent magnet generator only produces a signal if the drive wheels are turning greater than 3 mph (5 km/h). This step determines if DTC P0502 is the result of a hard failure or an intermittent condition.
3. Proper engine loads cannot be achieved in a shop environment to properly run the vehicle within the Freeze Frame Data conditions. It will be necessary to drive the vehicle on the road to obtain the proper engine loads.
4. This step verifies that the PCM is receiving a signal from the vehicle speed sensor.
5. Refer to service bulletin information for the latest calibration update.
6. Refer to the latest Tech line information for programming procedures.
8. A resistance reading that is higher than the specified value indicates that the VSS circuitry is open.
10. If the displayed resistance were less than the 1300 ohms, the VSS high and low circuits are shorted together. If the resistance value within the specified value, check the VSS high and low circuits for a short to ground.
11. This checks the resistance of the VSS if no opens or shorts were found on the VSS high and low circuits.
13. Replacement PCM must be reprogrammed. Refer to the latest Techline information for programming procedures.