WOMS
P code powertrain Medium severity

P1503 Auxillary Speed Sensor Fault

The OBD2 code P1503 indicates a fault with the auxiliary speed sensor, which is responsible for monitoring the vehicle's speed and providing input to the engine control module for various functions

Definition

The OBD2 code P1503 indicates a fault with the auxiliary speed sensor, which is responsible for monitoring the vehicle's speed and providing input to the engine control module for various functions

Common causes

  • Faulty auxiliary speed sensor
  • Damaged wiring or connectors
  • Poor electrical connections
  • Malfunctioning engine control module (ECM)
  • Incorrect sensor installation
  • Mechanical issues affecting sensor operation
  • Corrosion or dirt on sensor terminals

Common misdiagnoses

  • Faulty throttle position sensor
  • Malfunctioning mass air flow sensor
  • Ignition system issues
  • Vacuum leaks
  • Engine control module (ECM) problems
  • Transmission issues
  • Wiring or connector problems
  • Fuel delivery issues

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. Sometimes, multiple codes can provide more context for the issue

  2. 2. Inspect the Wiring and Connectors

    Visually inspect the wiring and connectors associated with the auxiliary speed sensor. Look for signs of damage, corrosion, or loose connections

  3. 3. Ensure that the connectors are securely attached and that there are no broken wires

  4. 4. Test the Auxiliary Speed Sensor

    Use a multimeter to test the resistance of the auxiliary speed sensor. Compare the readings to the manufacturer's specifications

  5. 5. If the sensor is faulty, it may need to be replaced

  6. 6. Check the Sensor's Signal

    With the vehicle running, use a scan tool to monitor the signal from the auxiliary speed sensor. Ensure that it is providing a valid speed reading

  7. 7. If the signal is erratic or absent, the sensor may be defective

  8. 8. Inspect the Vehicle's Speedometer

    Check if the speedometer is functioning correctly. If the speedometer is not working, it may indicate a problem with the speed sensor or related components

  9. 9. Examine the ECM/TCM

    If the sensor and wiring are in good condition, the issue may lie within the engine control module (ECM) or transmission control module (TCM). Check for software updates or faults in these modules

  10. 10. Check for Mechanical Issues

    Inspect the vehicle for any mechanical issues that could affect the speed sensor's operation, such as problems with the transmission or differential

  11. 11. Clear the Codes and Test Drive

    After performing repairs or replacements, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  12. 12. Consult the Service Manual

    Refer to the vehicle's service manual for specific diagnostic procedures and specifications related to the auxiliary speed sensor

  13. 13. Seek Professional Help

    If the issue persists after following these steps, consider seeking assistance from a qualified mechanic or automotive technician who can perform more advanced diagnostics. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P1503 code