P0503

Diagnostic Chart:

CIRCUIT DESCRIPTION

The Vehicle Speed Sensor (VSS) is a Permanent Magnet (PM) generator attached to the transmission case. The final drive assembly has a toothed wheel (VSS rotor). As the final drive assembly rotates, an AC voltage is induced and transmitted to the Powertrain Control Module (PCM). The PCM converts the AC voltage into a digital signal. The PCM uses vehicle speed to determine shift timing, Torque Converter Clutch (TCC) apply and release, and gear ratio. VSS voltage will vary from 0.5 volts AC at 100 RPM to more than 100 volts AC at 8000 RPM. VSS resistance value is between 1300-1950 ohms.

When the PCM detects a large change in vehicle speed, then DTC P0503 sets. DTC P0503 is a Type B DTC.

CONDITIONS FOR SETTING THE DTC

^ No MAF DTCs P0101, P0102 or P0103.

^ No TP Sensor DTCs P0121, P0122 or P0123.

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

^ No TFP Valve Position Switch DTC P1810.

^ The transmission is not in Park or Neutral.

^ The engine run time is greater than 5 seconds.

^ The engine is not in fuel cut off.

^ The time since the gear select lever change is greater than 3 seconds.

^ Traction control is inactive.

^ The engine speed is greater than 500 RPM.

^ The TP angle is greater than 12.8 degrees.

^ The delivered torque is greater than 109 N.m (80 lb. ft).

^ The vehicle speed drops greater than 18 km/h (11 mph) in 0.13 seconds and input speed does not drop by 100 RPM within 0.13 seconds. (This condition must occur 10 times within 10 seconds.)

ACTION TAKEN WHEN THE DTC SETS

^ The PCM illuminates the Malfunction Indicator Lamp (MIL).

^ SERVICE ENGINE SOON message displays on the Driver Information Center (DIC).

^ The PCM commands default line pressure.

^ The PCM inhibits TCC engagement.

^ The PCM disables the cruise control.

^ The PCM disables steady state adapts.

^ The PCM disables upshift adapts.

^ The PCM calculates vehicle speed from the Automatic Transmission Input (Shaft) Speed sensor and commanded gear.

^ DTC P0503 is stored in the PCM history.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The PCM turns OFF the MIL after three consecutive trips 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

^ Inspect the wiring for poor electrical connections at the PCM, the VSS 2-way connector and all other circuit connecting points 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

- Moisture intrusion

- Corrosion

^ Inspect the engine wiring harness for pinched wires which may cause an intermittent. When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.

^ Check for Electromagnetic Interference (EMI) induced on circuits 400 and 401 by a misrouted wiring harness along spark plug wires.

^ Ensure that the VSS is tightened securely into the transmission case extension.

TEST DESCRIPTION

The numbers below refer to the step numbers on the Diagnostic Table.

2. This step checks for DTCs. This step checks for a vehicle speed signal. It is important to record Freeze Frame and Failure Records information before proceeding further.

4. This step has the scan tool verify that the correct calibration is in the PCM.

6. This step tests for a resistance value greater than 1950 ohms. A resistance value greater than 1950 indicates a possible open in circuit 400 or 401.

8. This step tests for a resistance value less than or equal to the specified VSS value. A resistance less than 1300 indicates that the circuits are shorted together.

10. This step tests for a possible skewed VSS or PCM.