P0502

DTC P0502

CIRCUIT DESCRIPTION
The vehicle speed information is provided to the engine control module (ECM) by the vehicle speed sensor (VSS). The VSS is a permanent magnet generator that is mounted to the transmission and produces a pulsing voltage. The AC voltage amplitude and frequency increases with vehicle speed. The ECM converts the pulsing voltage into km/h (mph). The ECM supplies the VSS signal to the following components:
- The instrument panel for speedometer and odometer operation
- The cruise control module
- The multi-function alarm module

If the ECM detects no vehicle speed for a calibrated amount of time, this DTC sets.

DTC DESCRIPTOR
This diagnostic supports the following DTC:
DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Voltage

CONDITIONS FOR RUNNING THE DTC
- DTCs P0106, P0107, P0108, P0115, P0117, P0118, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0217, P0300, P0351, P0352, P0402, P0404, P0405, P0406, and P0488 are not set.
- The engine is running.
- The engine coolant temperature (ECT) is more than 60°C (140°F).
- The ignition 1 voltage is between 11-16 volts.
- The following are additional Conditions for Running for the applicable test:

Power Test
- The engine speed is between 1,200-4,000 RPM.
- The throttle position (TP) sensor is between 25-60 percent.
- The manifold absolute pressure (MAP) is more than 60 kPa.

Deceleration Test
- The MAP is less than 30 kPa.
- The change in engine speed per cycle is less than or equal to 50 RPM/cycle.
- The throttle position (TP) sensor is less than or equal to 0.8 percent.
- The engine speed is between 1,800-6,000.
- DTC P0502 runs continuously when the above conditions are met.

CONDITIONS FOR SETTING THE DTC
The ECM detects that the vehicle speed is less than 5 km/h (3.1 mph) for more than 35 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
- An intermittent condition may be caused by a poor connection, rubbed-through wire insulation, or a wire that is broken inside the insulation.
- Ensure the VSS is correctly torqued to the transmission housing.
- For an intermittent condition, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-2:

Steps 3-6:

Steps 7-8:

Steps 9-14:

Steps 15-16:

The numbers below refer to the step numbers on the diagnostic table.
2. The permanent magnet generator only produces a signal if the drive wheels are turning greater than 8 km/h (5 mph). This step determines if DTC P0502 is the result of a hard failure or an intermittent condition.