3T40 Automatic Transmission

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

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 (PM) generator. The PM generator produces an AC voltage as the speed sensor rotor teeth on the transmission governor assembly pass through the sensor 5 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 and there is a high engine speed in a drive range, then DTC P0503 sets. DTC P0503 is 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 re 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.

DIAGNOSTIC AIDS
^ Inspect for Electromagnetic Interferences (EMI) induced on circuit 400 and circuit 401 by an improperly routed harness.
^ Inspect the connectors at the PCM, the VSS 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.
^ Inspect the following components for proper operation:
- Speed sensor assembly housing
- Speed sensor rotor teeth
- Governor assembly and drive gear

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 checks for the VSS assembly ability to produce an AC voltage.
4. This step checks for correct circuit resistance.
6. When the VSS assembly is disconnected, the circuit resistance should be infinite.
9. This step checks 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.