With 4 Speed Automatic

Diagnostic Chart:

Wiring Diagram:

Circuit Description

The Automatic Transmission Output (Shaft) Speed Sensor (A/T OSS Sensor) provides vehicle speed information to the Powertrain Control Module (PCM). The A/T OSS Sensor is a Permanent Magnet (PM) generator mounted to the transmission case. The PM generator produces an AC voltage as the transmission speed sensor rotor teeth pass through the sensor's magnetic field. The AC voltage level increases as the speed of the vehicle increases. The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed signal to determine shift timing, Torque Converter Clutch (TCC) apply, TCC release, and gear ratio calculations.

When the PCM detects a low output speed and the vehicle has a large engine speed in a drive gear, then DTC P0502 sets. DTC P0502 is a type B DTC.

Conditions for Setting the DTC

^ The transmission is in a drive range.

^ No MAP DTCs P0107 or P0108

^ No Throttle position (TP) Sensor DTCs P0121, P0122, or P0123

^ No Automatic Transmission Input Speed (A/T ISS) sensor DTCs P0716 or P0717.

^ No engine torque DTC P1644

^ No Automatic Transmission Fluid Pressure Manual Valve Position Switch (TFP Val. Position Sw.) DTC P1810

^ The TP angle is 15-99%.

^ The MAP is greater than 20 kPa.

^ The input speed is greater than 1000 RPM.

^ The output speed is less than 3.2 km/h (2 mph).

^ All of the above conditions are met for 5 seconds.

Action Taken When the DTC Sets

^ The PCM illuminates the Malfunction Indicator Lamp (MIL) after two consecutive trips with a failure reported.

^ The PCM freezes shift adapts from being updated.

^ The PCM commands maximum line pressure.

^ The PCM calculates output speed from input speed, engine speed, and commanded gear.

^ DTC P0502 is stored in the PCM history.

Conditions for Clearing the MIL/DTC

^ The PCM turns OFF the MIL after three consecutive ignition cycles without a failure reported.

^ A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

Diagnostic Aids

^ The condition may be intermittent. Inspect for a loose A/T OSS sensor, or poor sensor connection.

^ Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring for poor electrical connections at the transmission 20-way connector. Look for the following conditions:

- A bent terminal

- A backed out terminal

- A damaged terminal

- Poor terminal tension

- A chafed wire

- A broken wire inside the insulation

^ When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.

^ Inspect for a damaged A/T OSS Sensor. Inspect for damaged transmission rotor teeth.

^ A slipping forward clutch could set DTC P0502.

Test Description

The numbers below refer to the Step numbers on the diagnostic table.

2. This Step tests for a signal from the A/T OSS Sensor.

3. This Step tests the ability of the A/T OSS Sensor to produce an AC voltage.

4. This Step measures for correct circuit resistance from the PCM connectors to the A/T OSS Sensor.

7. When the A/T OSS Sensor is disconnected, circuit resistance should be infinite.

10. This Step tests for improper voltage in the circuit.

15. This Step inspects the A/T OSS Sensor and the A/T OSS Rotor for mechanical failure.

17. This Step replaces the PCM after testing the component and circuitry.