1996 Pontiac Grand Am DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input (3.1L VIN M) Service Manual

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Action Taken When the DTC Sets Conditions for Clearing the MIL/DTC Diagnostic Aids Test Description The numbers below refer to the step numbers on the diagnostic table. 2. This step verifies that the PCM is receiving a signal from the vehicle speed sensor. 3. This step verifies that there are no opens in the circuitry from the vehicle speed sensor to the PCM connector. 7. This step performs a resistance test on the VSS circuits from the PCM connector. • The transmission defaults to 3rd gear. • The PCM inhibits TCC operation. • The PCM illuminates the Malfunction Indicator Lamp (MIL). • 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. • Check for PRNDL DTC P0705. DTC P0705 affects transmission operation. This may set DTC P0502 falsely. • Check for Electromagnetic Interference (EMI) in circuits 400 and 401. EMI may be induced if the harness is routed along the spark plug wires. • Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring at the TCC brake switch. 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. • Ensure that the VSS is securely tightened to the case extension. DTC P0502 Vehicle Speed Sensor Circuit (VSS) Low Input