4L80-E / 4L85-E Automatic Transmission

DTC P0502





Circuit Description with 4L80-E / 4L85-E Automatic Transmission
The automatic transmission output shaft speed(AT OSS) sensor, which is a permanent magnet generator, produces an AC voltage as the transmission speed sensors rotor teeth pass through the magnetic field of the sensor. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The powertrain control module (PCM) converts the voltage to a digital signal for vehicle speed. The vehicle speed is used for engine and transmission calculations.

If the PCM detects a low vehicle speed and there is a high engine speed in a drive gear range, DTC P0502 sets. DTC P0502 is a type C DTC. For California emissions and vehicles under 8,600 GVW, DTC P0502 is a type B DTC.

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

Conditions for Running the DTC
^ No MAF sensor DTC P0101, P0102 or P0103.
^ No MAP sensor DTC P0106, P0107 or P0108.
^ No TP sensor DTC P0121, P0122 or P0123.
^ No VSS DTC P0503.
^ No ISS DTC P0716 or P0717.
^ No TFP manual valve position switch DTC P1810.
^ The engine torque must be 108 - 576 Nm (80 - 425 ft. lbs.).
^ No change in 4WD low for at least 2 seconds.
^ The input speed is greater than 1,400 RPM.
^ The gear range is not PARK or NEUTRAL.
^ The system voltage is between 8-18 volts for more than 5 seconds.
^ Throttle angle is equal to or greater than 10 percent.
^ The engine vacuum is 0-105 kPa (0-15 psi).
^ The engine is running greater than 400 RPM for more than 7 seconds.

Conditions for Setting the DTC
The AT OSS is less than 50 RPM for at least 3.5 seconds.

Action Taken When the DTC Sets
^ For California emission equipped vehicles, the PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. For Federal emission equipped vehicles, the MIL is not illuminated.
^ The PCM commands maximum line pressure.
^ The PCM freezes transmission adaptive functions.
^ The PCM defaults a calculated output speed value by using the automatic transmission input shaft speed(AT ISS) values.
^ The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame, California only, and Failure Records, California and Federal.
^ The PCM stores the DTC P0502 in PCM history during the second consecutive trip, California, or the first trip, Federal, in which the Conditions for Setting the DTC are met.

Conditions for Clearing the MIL/DTC
^ For California emissions, 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.
^ For California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
^ For Federal emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without a non-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
DTC P0502 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine.

Test Description








The numbers below refer to the step numbers on the diagnostic table.
3. This step tests the OSS/VSS assembly circuit.
4. This step tests the integrity of the OSS assembly.