P0502

DTC P0502 VSS Circuit Low Input




Circuit Description
The vehicle speed sensor has a magnet rotated by the transmission output shaft. Attached to the sensor is a hall effect circuit the interacts with the magnetic field treated by the rotating magnet. A 12-volt operating supply for the speed sensor hall circuit is supplied from the meter fuse. The VSS pulses to ground the 9-volt signal sent from the powertrain control module (PCM) on the reference circuit. The PCM interprets vehicle speed by the number of pulses to ground per second on the reference circuit.

Conditions for Setting the DTC
- Engine is running.
- Engine coolant temperature is above 60 °C (140 °F).
- Engine speed is between 1800 RPM and 2500 RPM.
- Throttle angle is between 10% and 40%.
- Engine load is greater than 50 kPa.
- MAP sensor indicates greater than 50 kPa manifold pressure.
- PCM detects no VSS signal for 12.5 seconds over a period of 25 seconds.

Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp (MIL) the first time the fault is detected.
- The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.

Conditions for Clearing the MIL/DTC
- The PCM will turn the MIL OFF on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
- A history DTC P0502 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P0502 can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Steps 1 - 6:

Steps 7 - 10:

Steps 11 - 13:

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
9. To avoid backprobing the VSS and possibly damaging a seal or terminal, the VSS output can be tested at the point where the transmission harness connected to the engine harness. The green 16-way connector is adjacent to a blue 16-way connector, and it can be easily accessed by removing the air cleaner assembly. The green 16-way connector is separated, and battery voltage is applied to the VSS through the yellow wire at one corner of the connector. The VSS output can be monitored with a DVM connected to the blue wire with a black tracer. The two wires are next to each other in the 16-way connector. The test connections are made on the transmission side of the connector, the side that is not clipped to the body sheetmetal.
14. The speedometer-to-PCM VSS signal wire is spliced to a wire leading to the cruise control module. If a short to ground or voltage is found between the PCM and speedometer, it could be located between the splice and the cruise control module.