4L80-E / 4L85-E Automatic Transmission
DTC P0503
Circuit Description
The automatic transmission output shaft speed (AT OSS) sensor, which is a permanent magnet generator, produces a pulsing 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) then converts the pulsing 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 P0503 sets. DTC P0503 is a type C DTC. For California emissions and vehicles under 8,600 GVW, DTC P0503 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0503 Vehicle Speed Sensor (VSS) Circuit Intermittent
Conditions for Running the DTC
^ No TFP manual valve position switch DTC P1810.
^ The engine is running greater than 400 RPM for greater than 7 seconds.
^ The system voltage is between 8 - 18 volts for greater than 0.5 second.
^ No TFP manual valve position switch changes for greater than 6 seconds.
^ No 4WD low switch change within 2 seconds.
^ No AT OSS increase greater than 250 RPM within 2 seconds.
Conditions for Setting the DTC
^ The gear range is not PARK or NEUTRAL.
^ The AT VSS RPM has dropped greater than 1,000 RPM for at least 3.4 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 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 P0503 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 P0503 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 assembly circuit.
4. This step tests the integrity of the OSS assembly.
