P0502

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The Vehicle Speed Sensor (VSS) system is a pulse generator consisting of a speed sensor assembly, located in the case extension, and a toothed vehicle speed sensor reluctor wheel, which is pressed onto the final drive carrier assembly. As the vehicle drives forward, the vehicle speed sensor reluctor wheel rotates. This rotation produces a variable AC signal in the pickup coil that is proportional to vehicle speed.

The AC signal generated has a frequency and amplitude (voltage). The PCM uses the frequency to calculate the vehicle speed. The voltage portion of the signal is used for diagnostic purposes only. The voltage will vary from 0.5 volts AC at 100 RPM to as much as 200 volts AC at 6000 RPM.

This information is then sent to the PCM to indicate how fast the vehicle is traveling and to develop the shift pattern for the transmission. Other systems also use VSS information:
^ TCC apply and release
^ Cruise control system
^ Fuel delivery systems

If the PCM detects a low vehicle speed with a high engine speed while in a drive range, then DTC P0502 sets. DTC P0502 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
^ No MAP sensor DTC P0106, P0107, P0108, P1106 or P1107.
^ No TP sensor DTC P0121, P0122, P0123, P1121 or P1122.
^ No AT ISS DTC P0716 or P0717.
^ No TFP manual valve position switch DTC P1810.
^ The TP angle is greater than 12%.
^ The MAP is 0-105 kPa (0-15 psi).
^ The engine torque is 55-400 N.m (40-300 lb ft).
^ The transmission is not in PARK or NEUTRAL.
^ The input shaft speed is greater than 1500 RPM.

CONDITIONS FOR SETTING THE DTC
The output shaft speed is less than 150 RPM for 2.5 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 shift adapts.
^ The PCM calculates vehicle speed from the AT input shaft speed sensor for shift timing.
^ 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 clears the DTC from the PCM history.
^ The PCM clears the DTC from the PCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related diagnostic fault occurring.
^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

DIAGNOSTIC AIDS
^ Inspect the connectors at the controller, the component and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Diagrams.
^ Check for Electromagnetic Interference (EMI) in circuits 400 (YEL) and 401 (PPL). EM may be induced by a misrouted wiring harness along the spark plug wires.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
3. This step tests the ability of the VSS to produce an AC current. This step also verifies the integrity of the wiring to the PCM.
4. This step tests the VSS circuit for correct resistance.