P0502

Steps 1 - 5:

Steps 6 - 10:

DTC P0502 Vehicle Speed Sensor (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 that interacts with the magnetic field created 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 5-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. DTC P0502 is a type B code.

Conditions for Setting the DTC
- Engine is running.
- Engine coolant temperature is above 60 °C (140 °F).
- System voltage is between 10 and 16 volts.

When the above conditions are met, one of the following tests will run:

Decel Test
- MAP is less than 35 kPa.
- Throttle Position is less than 0.8 %.
- Engine Speed is between 1500 RPM and 3500 RPM.

The Decel Test will fail if vehicle speed is less than 8 kph (5 mph).
The Decel Test will pass if vehicle speed is greater than 24 kph (15 mph).

Power Test
- MAP is greater than 50 kPa.
- Throttle Position is between 25 % and 70 %.
- Engine Speed is between 2700 RPM and 4400 RPM.

The Power Test will fail if vehicle speed is less than 8 kph (5mph).
The Power Test will pass if vehicle speed is greater than 8 kph (5mph) without any VSS

DTC's present, or if vehicle speed is greater than 49 kph (30 mph) with VSS Diagnostic Trouble Codes present.

Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp (MIL) the second time the fault is detected.
- Base shift logic on RPM only.
- The PCM will store conditions which were present when the Diagnostic Trouble Code 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 Diagnostic Trouble Code P0502 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- Diagnostic Trouble Code P0502 can be cleared by using the Scan Tool's "Clear Info" function.

Diagnostic Aids
- Poor connection at PCM: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- Damaged harness: Inspect the wiring harness to the EVAP vent solenoid, the EVAP purge solenoid, and the fuel tank pressure sensor for an intermittent open or intermittent short circuit.