3T40 Automatic Transmission

DTC P0503





Test 1-8





Test 9-15

Circuit Description with 3T40 Automatic Transmission
The Vehicle Speed Sensor (VSS) assembly provides vehicle speed information to the Powertrain Control Module (PCM). The VSS assembly is a permanent magnet generator. The VSS assembly produces an AC voltage as the speed sensor rotor teeth on the transmission governor assembly pass through the sensor's magnetic field. The AC voltage level and the number of pulses increases as the speed of the vehicle increases. The output voltage varies from a minimum of 0.5 volts AC at 25 RPM to more than 100 volts AC at 200 RPM. The PCM converts the pulsing voltage to vehicle speed. The PCM uses the vehicle speed signal to calculate Torque Converter Clutch (TCC) scheduling.
When the PCM detects a loss of vehicle speed with high engine speed in a drive range, then DTC P0503 sets. DTC P0503is a type B DTC.

Conditions for Running the DTC
^ Engine is running.
^ Time since the last gear select lever change is greater than 6 seconds.
^ Transmission output speed is greater than 500 RPM for 5 seconds.

Conditions for Setting the DTC
Transmission output speed drops more than 1200 RPM in a drive range for 4 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.
^ TCC will not apply.
^ The PCM stores DTC P0503 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 consecutive warm-up cycles without an emission-related fault occurring.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for a vehicle speed signal.
3. This step tests for the VSS assembly ability to produce an AC voltage.
4. This step tests for correct circuit resistance.
6. When the VSS assembly is disconnected, the circuit resistance should be infinite.
9. This step tests for improper voltage in the circuit.
12. This step inspects for possible mechanical problems.
14. Replace the PCM only after you have completed the preceding diagnostic steps.