P0502

Diagnostic Chart:

Diagnostic Chart (cont'd):

Wiring Diagram:

CIRCUIT DESCRIPTION

The Vehicle Speed Sensor (VSS) provides vehicle speed information to the PCM. The VSS is a Permanent Magnet (PM) generator. The VSS produces a pulsing AC voltage. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The PCM converts the voltage pulses to vehicle speed. A scan tool can display the calculated 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 A DTC.


CONDITIONS FOR SETTING THE DTC

- No MAP DTCs P0107 or P0108.

- No Throttle Position (TP) DTCs P0122 or P0123.

- No TFP Valve Position Switch DTC P1810.

- Not in Park or Neutral.

- The TP angle is greater than 20%.

- The engine vacuum is 0-106 kPa.

- The engine speed is greater than 4000 RPM.

- The engine torque is 40-400 lb. ft.

- The transmission output speed is less than 150 RPM.

- All conditions met for 2.5 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 Solenoid Valve 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

- A VSS DTC P0502 will set when no vehicle speed is detected at start OFF.

- 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 test equipment for changes.

- Test circuits 400 and 401 for Electromagnetic Interferences (EMI) induced by a wiring harness incorrectly routed too near the spark plug wires.

- Incorrect VSS calibration may set DTC P0502. Refer to Service bulletins to ensure that the calibration is current.

- Inspect for a damaged VSS or transmission rotor teeth.

- Ensure that the VSS is correctly aligned and torqued securely to the transmission case.


TEST DESCRIPTION

The numbers below refer to the step numbers on the diagnostic chart.

3. Step 3 verifies the integrity of the VSS.

4. Step 4 verifies the integrity of the VSS circuit.

8. Step 8 tests the resistance of the VSS.