What causes a P1303 code?

P1303 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 P1303 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1303 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

P1303

Intermittent misfire cylinder 3

What it means

The Engine Control Module (ECM) has detected an inconsistent or occasional misfire event specifically in cylinder number 3 based on crankshaft speed fluctuations.