What does code P1503 mean?

Q: What does code P1503 mean?

Auxiliary Speed Sensor Fault. P1503 on GM vehicles indicates that the powertrain control module (PCM) has detected a fault in the auxiliary speed sensor circuit, which typically monitors the speed of a secondary component such as the transmission output shaft or transfer case. The PCM sets this code when the sensor signal is missing, erratic, or out of range compared to other speed inputs, often affecting speedometer accuracy and shift scheduling.

DTC codes / GM codes / P1503

P1503 · GMAuxiliary Speed Sensor Fault

P1503 on GM vehicles indicates that the powertrain control module (PCM) has detected a fault in the auxiliary speed sensor circuit, which typically monitors the speed of a secondary component such as the transmission output shaft or transfer case. The PCM sets this code when the sensor signal is missing, erratic, or out of range compared to other speed inputs, often affecting speedometer accuracy and shift scheduling.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.