What causes a P1503 code?

P1503 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a P1503 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1503 active.

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

OBD-II

P1503

Vehicle speed sensor short circuit to battery voltage

What it means

The ECM has detected a voltage signal on the Vehicle Speed Sensor (VSS) circuit that is higher than expected, specifically matching battery voltage (12V+).