What causes a P1204 code?

P1204 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 P1204 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1204 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

P1204

Cylinder 1: Injector needle valve low side short circuit to battery voltage

What it means

The ECM has detected battery voltage on the return (low side) circuit of the number 1 fuel injector, indicating a short to power that prevents the ECM from controlling the opening/closing of the injector.