P0502

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION
The Output Shaft Speed Sensor (OSS Sensor), which is a Permanent Magnet (PM) generator, gives the vehicle speed information to the Vehicle Control Module (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.
If 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 B DTC.

CONDITIONS FOR SETTING THE DTC
^ No Throttle Position (TP) Sensor DTCs P0122 or P0123.
^ No TFP Val. Position Sw. DTC P1810.
^ No Automatic Transmission Input Speed Shaft (A/T ISS) Sensor low DTC P0716 or P0717.
^ The engine torque must be 60 Nm (80 lb. ft) to the following:
- 470 Nm (375 lb. ft) 5.7L.
- 627 Nm (500 lb. ft) 7.4L.
^ The A/T ISS is greater than 2500 RPM.
^ The transmission is not in Park or Neutral.
^ The engine is running more than 475 RPM for 7 seconds.
^ The OSS 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 problems:
- 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, 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.
4. This step tests for voltage in the 822 ground circuit.
6. This step tests the 5-volt and ground circuit of the VCM.
11. This step tests the integrity of the OSS Sensor.
13. This step tests the OSS circuit.