P0503

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Vehicle Speed Sensor Assembly (VSS Assy.) provides vehicle speed information to the Vehicle Control Module (VCM). 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 VCM converts the pulsing voltage to vehicle speed. The VCM uses the vehicle speed signal to determine shift timing and Torque Converter Clutch (TCC) scheduling. When the VCM 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 engine speed is greater than 450 RPM for 5 seconds.

^ Not in fuel cutoff.

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

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

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

ACTION TAKEN WHEN THE DTC SETS

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

^ The VCM commands second gear only.

^ The VCM commands maximum line pressure.

^ The VCM freezes shift adapts from being updated.

^ The VCM inhibits TCC engagement.

^ DTC P0503 stores in VCM history.

CONDITIONS FOR CLEARING THE MIL/DTC

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

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

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

DIAGNOSTIC AIDS

^ Inspect the wiring at the VCM, 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.

8. This step tests the 5-volt and ground circuit of the VCM.