P0503

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Vehicle Speed Sensor Assembly (VSS Assy.) provides vehicle speed information to the Powertrain Control Module (PCM). The VSS Assy. is a Permanent Magnet (PM) generator. The PM generator produces a pulsing Idle Air Control (IAC) voltage as rotor teeth on the transmission output shaft pass through the sensor's magnetic field. The IAC voltage level and the number of pulses increase as the speed of the vehicle increases. The output voltage varies from a minimum of 0.5 volts IAC at 100 RPM to more than 100 volts at 8000 RPM. The PCM converts the pulsing voltage to vehicle speed. The PCM uses the vehicle speed signal to determine shift timing and Torque Converter Clutch (TCC) scheduling.

When the PCM detects an unrealistically large drop in vehicle speed, then DTC P0503 sets. DTC P0503 is a type B DTC.

CONDITIONS FOR SETTING THE DTC

DTC P0503 sets if the following conditions occur two consecutive times:

^ No Transmission Fluid Pressure (TFP) Val. Position Sw. DTC P1810.

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

^ The engine speed is greater than 450 RPM for 5 seconds.

^ Not in fuel cutoff.

^ Transmission output speed rise does not exceed 600 RPM within 6 seconds.

^ The transmission output speed drop is greater than 1300 RPM for 3 seconds when not in Park/Neutral.

ACTION TAKEN WHEN THE DTC SETS

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

^ The PCM commands a soft landing to second gear when the engine speed is below 2500 RPM.

^ The PCM commands maximum line pressure.

^ The PCM inhibits TCC engagement.

^ The PCM freezes shift adapts from being updated.

^ The PCM inhibits 4th gear if the transmission is in hot mode.

^ DTC P0503 stores in PCM history.

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.

^ 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.

3. This step tests the VSS Assy. circuit.

5. This step tests the integrity of the VSS Assy.