P0503

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 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.

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

Conditions for Running the DTC

^ No MAF DTCs P0101, P0102 or P0103.
^ No TP DTCs P0121, P0122 or P0123.
^ No A/T Input (shaft) Speed Sensor (ISS) DTCs P0716 or P0717.
^ No Transmission Fluid Pressure (TFP) manual 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).

Conditions for Setting the DTC

The vehicle speed drops greater than 18 km/h (11 mph) in 0.13 seconds and the input speed does not change by more than 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) during the second consecutive trip in which the Conditions for Setting the DTC are met.
^ SERVICE ENGINE SOON, SPEED SENSOR FAULT 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 freezes steady state adapts.
^ The PCM freezes upshift adapts.
^ The PCM calculates vehicle speed from the automatic transmission input (shaft) speed sensor and commanded gear.
^ 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 clears the DTC from PCM history.
^ The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an 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

^ Inspect the wiring at the PCM and the VSS 2-way connector for the following conditions:
- A backed out terminal
- A damaged terminal
- Reduced terminal tension
- A chafed wire
- A broken wire inside the insulation
- Moisture intrusion
^ 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 and for a vehicle speed signal. It is important to record Freeze Frame and Failure Records information before proceeding further.
4. This step tests for a resistance value greater than 1950 ohms which would indicate a possible open in circuit 400 or circuit 401.
6. This step tests for a resistance value less than or equal to the specified VSS value. Resistance less than 1300 implies that the circuits are shorted together. Resistance within specification implies that circuit 400 or circuit 401 has a possible short to ground.
8. This step performs a resistance check on the VSS if you found no opens, shorts to ground, or shorts together on circuit 400 or circuit 401.