Transmission Diagnosis

P0502 - VEHICLE SPEED SENSOR (VSS) CIRCUIT LOW (L61)









The Output Speed Sensor (OSS) produces an AC voltage of different amplitude and frequency depending on the velocity of the output shaft. The OSS produces the signal from 16 evenly spaced machined notches on the transaxle final drive assembly. The OSS produces a readable AC voltage signal when vehicle speed is above 5 km/h (3 mph). This VSS signal is sent to the PCM, which is used to determine the velocity of the output shaft. DTC P0502 sets when the PCM does not detect a VSS signal for a certain length of time.

DTC PARAMETERS
DTC P0502 will set if TRANSMISSION OSS signal is less than 100 RPM when:
- Condition exists for longer than 3 seconds.
- Transaxle is not is Park/Neutral.
- Engine torque is between 68 and 406 Nm (50 and 300 ft. lbs.).
- MAP is between 0 - 104 kPa.
- TP angle is greater than 12%
- No ISS, MAP, TP sensor or P1810 DTCs have been set.

DTC P0502 diagnostic runs continuously once the above conditions have been met.
P0502 is a type B DTC.

DIAGNOSTIC AIDS
To locale an intermittent problem. use Scan tool to monitor VEHICLE SPEED or TRANSMISSION OSS with vehicle raised and drive wheels moving greater than 5 km/h (3 mph). Wiggling wires while watching for a change in VEHICLE SPEED or TRANSMISSION OSS may locale the area where an open or short to ground in the wiring could lie.
If TRANSMISSION OSS signal is received, the speedometer will be inoperative. Once P0502 is set, the speedometer will be inoperative for the rest of the ignition cycle even if a valid signal is later received.
If the PCM does not receive a TRANSMISSION OSS signal it will command maximum main line pressure to the transaxle. Shift timing will be affected as well.
Output Speed Sensor Resistance: 1530 - 1870 ohms