P0502

DTC P0502

Vehicle Speed Sensor (VSS) Schematic:

Circuit Description
The Vehicle Speed Sensor (VSS) is a permanent magnet generator attached to the transmission case. The final drive assembly has a toothed wheel, VSS rotor. As the final drive assembly rotates, an AC voltage is induced and transmitted to the PCM. The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed to determine shift timing, torque converter clutch apply and release, and gear ratio.
If the PCM detects a low vehicle speed and a high transmission input shaft speed while in a drive range, then DTC P0502 sets. DTC P0502 is a type B DTC.

Conditions for Running the DTC
- No TP DTCs P0121, P0122 or P0123.
- No VSS DTC P0503.
- No AT ISS DTCs P0716 or P0717.
- No IMS DTCs P1820, P1822, P1823, or P1825.
- The system voltage is 8 - 18 volts.
- The engine run time is greater than 5 seconds.
- The transmission is not in PARK or NEUTRAL.
- The TP angle is 12 percent or greater.
- The engine torque is 60 - 395 Nm (44 - 291 ft. lbs.).
- The transmission input shaft speed is 1,000 - 5,000 RPM.

Conditions for Setting the DTC
- LD8: The transmission output shaft speed is 280 RPM or less for 3 seconds.
- L37: The transmission output shaft speed is 334 RPM or less for 3 seconds.

Action Taken When the DTC Sets
- The PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
- The PCM commands maximum line pressure.
- The PCM freezes transmission adapt functions.
- The PCM calculates vehicle speed from the automatic transmission input, shaft, speed sensor and commanded gear.
- The PCM applies the TCC in 3rd gear when in Hot Mode.
- The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
- The PCM stores DTC P0502 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

Conditions for Clearing the MIL/DTC
- The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
- A scan tool can clear the MIL/DTC.
- The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
- The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM.

Test Description

Steps 1-8:

Steps 9-15:

The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for DTCs and for a vehicle speed signal. It is important to record Freeze Frame and Failure Record information before proceeding further.
5. This step tests for a resistance value greater than 1,950 ohms which would indicate an open in the high signal circuit, the low signal circuit or the VSS.