P0502

Diagnostic Chart:

Diagnostic Chart (cont'd):

Wiring Diagram:

Circuit Description
The Output Speed (OSS) Sensor, which is a Permanent Magnet (PM) generator, gives the vehicle speed information to the VCM. The PM generator produces a pulsing AC voltage. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The VCM then converts the pulsing voltage to vehicle speed. The vehicle speed is used for calculations. A scan tool can display the vehicle speed.

When the VCM detects a low vehicle speed and there is a high engine speed in a drive gear range, DTC P0502 sets. DTC P0502 is a type D DTC. For California emissions, DTC P0502 is a type A DTC.

Conditions for Setting the DTC

^ No Throttle Position (TP) Sensor DTCs P0122 or P0123.
^ No Transmission Fluid Pressure (TFP) Val. Position Sw. P1810.
^ No Input Speed (ISS) Sensor low DTC P0717.
^ The engine torque must be 100 N.m (80 lb. ft) to the following:

- 470 N.m (375 lb. ft).

^ The Input speed is greater than 2500 RPM.
^ The transmission is not in Park or Neutral.
^ The engine is running and not in fuel cut off.
^ The output shaft speed is less than 200 RPM for at least 3 seconds.

Action Taken When the DTC Sets

^ The VCM commands maximum line pressure.
^ The VCM freezes the shift adapts.
^ The VCM defaults a calculated output speed value by using the Input Speed Sensor values.
^ For California emissions, the VCM illuminates the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the MIL/DTC

^ For California emissions, the VCM turns off the MIL after three consecutive ignition cycles 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 cycled "off" long enough to power down the VCM.

Diagnostic Aids

^ DTC P0502 sets when no vehicle speed is detected at the start off.
^ Inspect the wiring for poor electrical connections at the VCM. Inspect the wiring for poor electrical connections at the transmission 20-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.
^ First diagnose and clear any engine DTCs or TP Sensor codes. Then inspect for any transmission DTCs that may have reset.

Test Description
The numbers below refer to the step numbers on the diagnostic table.

6. This step tests the Vehicle Speed Sensor (VSS) circuit.
7. This step tests the integrity of the VSS.
9. This step tests the 5-volt and ground circuit of the VCM.