Transmission Code

Diagnostic Chart:

Wiring Diagram:

Circuit Description
The Vehicle Speed Sensor Assembly (VSS Assy.) provides vehicle speed information to the PCM. The VSS Assy. is a Permanent Magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and the number of pulses increase with the speed of the vehicle. The PCM then converts the pulsing voltage to vehicle speed. The PCM uses this information for calculations. A scan tool can display the vehicle speed.

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

Conditions for Setting the DTC
DTC P0502 sets if the following conditions occur two consecutive times:

^ No MAP DTCs P0107 or P0108.
^ No Throttle Position (TP) DTCs P0122 or P0123.
^ No Transmission Fluid Pressure Manual Valve Position Switch (TFP Val. Position Sw.) DTC P1810.
^ The transmission is not in Park or Neutral.
^ The TP angle is 20-50%.
^ The engine torque is 0-1500 lbs. ft.
^ The engine speed is 3200-4800 RPM.
^ MAP is 25-45 kPa.
^ The vehicle speed is less than 3 km/h (2 mph).
^ All conditions met for 3 seconds.

Action Taken When the DTC Sets

^ The PCM commands second gear only.
^ The PCM commands maximum line pressure.
^ The PCM freezes shift adapts from being updated.
^ The PCM inhibits TCC engagement.
^ 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. 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 chart.

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