P0503

Diagnostic Chart:

Circuit Description

The Vehicle Speed Sensor (VSS) is a Permanent Magnet (PM) generator attached to the transmission case extension The final drive assembly has a toothed wheel (VSS rotor). As the final drive assembly rotates, an AC voltage is induced and transmitted to the Powertrain Control Module (PCM).

The PCM converts the induced AC voltage into a digital signal. The PCM uses the vehicle speed in order to determine the shift timing, the TCC apply and release, and the gear ratio calculations. The VSS voltage varies from 0.5 volts AC at 100 RPM to more than 100 volts AC at 6000 RPM. The VSS resistance is 981-1864 ohms.

When the PCM detects a low vehicle speed with a high engine speed while in a drive range, then DTC P0503 sets. DTC P0503 is a type A DTC.

Conditions for Setting the DTC

^ The engine speed is more than 500 RPM for 5 seconds.

^ The engine is not in fuel shut off.

^ More than 6 seconds has elapsed since the last gear change.

^ The output speed does not rise more than 1000 RPM within 2 seconds.

^ The transmission is not in Park or Neutral.

^ The output speed drops more than 1500 RPM within 2 seconds.

Action Taken When the DTC Sets

^ The transmission defaults to 3rd gear.

^ The PCM inhibits TCC operation.

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

Conditions for Clearing the MIL/DTC

^ The PCM turns OFF the MIL after three consecutive ignition cycles 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 for poor electrical connections at the PCM. Inspect the wiring at the transmission 7-way connector. Look 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 When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.

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

5. This step verifies that no opens exist in the circuitry from the vehicle speed sensor to the PCM connector.

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