With 3 Speed Automatic

Diagnostic Chart:

Wiring Diagram:

Circuit Description

Vehicle speed is provided to the Powertrain Control Module (PCM) by the Vehicle Speed Sensor Assembly (VSS Assy.), which is a Permanent Magnet (PM) generator mounted to the transmission case. The PM generator produces an AC voltage as the transmission's speed sensor rotor teeth pass in front of the sensor's magnet. The AC voltage level increases as the speed of the vehicle increases. The PCM converts the AC voltage into a digital signal. The PCM uses the signal to calculate the vehicle speed, and when to apply the Torque Converter Clutch (TCC).

When the PCM detects a low vehicle speed and there is a high engine speed in a drive range, then DTC P0502 sets. DTC P0502 is a type A DTC.

Conditions for Setting the DTC

^ No MAP DTCs P0107 or P0108

^ No Throttle position (TP) DTCs P0122 or P0123

^ No Vehicle Speed Sensor (VSS) Assy. DTC P0503.

^ The transmission is in a drive range.

^ The TP angle is greater than 12%.

^ MAP is greater than 50 kPa.

^ The engine speed is 2500-4775 RPM.

^ The vehicle speed is less than 3.2 km/h (2 mph).

^ All of the above conditions are met for four seconds.

Action Taken When the DTC Sets

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.

Diagnostic Aids

^ Inspect for Electromagnetic Interferences (EMI) induced on circuit 400 and circuit 401 by an improperly routed harness.

^ Brake Torquing the vehicle could set a DTC P0502.

^ Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring for poor electrical connections at the VSS Assy. 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 tests for a vehicle speed signal.

3. This Step checks for the VSS Assy. ability to produce an AC voltage.

4. This Step checks for correct circuit resistance.

7. When the VSS Assy. is disconnected, the circuit resistance should be infinite.

10. This Step checks for improper voltage in the circuit.

15. This Step inspects for possible mechanical problems.

17. Replace the PCM only after you have completed the preceding diagnostic steps.