P0503

Diagnostic Chart:

CIRCUIT DESCRIPTION

The Vehicle Speed Sensor (VSS) system is a pulse generator consisting of a speed sensor assembly, located in the case, and a toothed speed sensor rotor, which is pressed onto the final drive assembly. As the vehicle drives forward, the speed sensor rotor also rotates. This rotation produces a variable voltage signal in the pickup coil that is proportional to vehicle speed.

The VSS will generate AC voltage that will vary from 0.5 volts at 100 RPM to more than 100 volts at 6000 RPM.

This information is then sent to the PCM to indicate how fast the vehicle is traveling and to develop the shift pattern for the transmission. Other systems also use VSS information:

^ Torque Converter Clutch (TCC) apply and release

^ Cruise control system

^ Fuel delivery systems

If the PCM detects a large change in vehicle speed, in a short period of time, then DTC P0503 sets. DTC P0503 is a Type B DTC.


CONDITIONS FOR SETTING THE DTC

^ The transmission is not in Park or Neutral.

^ The time since the last gear range change is more than 6 seconds.

^ The engine speed is more than 500 RPM, for 5 seconds, and not in fuel shut off.

^ No output speed rise greater than 500 RPM in 2 seconds.

^ The output speed drops more than 1500 RPM in 3 seconds.


ACTION TAKEN WHEN THE DTC SETS

^ The PCM illuminates the Malfunction Indicator Lamp (MIL).

^ The PCM disables shift adapts.

^ The PCM commands maximum line pressure.

^ The PCM calculates vehicle speed from the Automatic Transmission Input Speed Sensor (A/T ISS) and from the commanded gear.


CONDITIONS FOR CLEARING THE MIL/DTC

^ The PCM turns OFF the MIL after three consecutive trips without a failure reported.

^ A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

DIAGNOSTIC AIDS

^ Inspect the wiring at the PCM, the Vehicle Speed Sensor (VSS) connector and all other circuit connecting points for the following conditions:

- A bent terminal

- A backed out terminal

- A damaged terminal

- Poor terminal tension

- A chafed wire

- A broken wire inside the insulation

- Moisture intrusion

- Corrosion

^ Inspect the engine wiring harness for pinched wires which may cause an intermittent. When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.

^ Check for an Electromagnetic Interference (EMI) induced on circuits 400 and 401 by a misrouted wiring harness along the spark plug wires.

^ Ensure that the VSS is tightened securely into the transmission case extension.

^ Too much runout in the final drive carrier may set DTC P0503. If you cannot find a condition with the VSS or its circuitry, replace the final drive carrier.

TEST DESCRIPTION

The numbers below refer to the step numbers on the Diagnostic Table.

2. This step verifies that the PCM is receiving a signal from the vehicle speed sensor.

3. This step verifies that there are no opens in the circuitry from the vehicle speed sensor to the PCM connector.

4. This step performs a resistance test on the VSS circuits from the PCM connector.