What causes a P1234 code?

P1234 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 P1234 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1234 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

P1234

Cylinder 5: Injector spill valve short circuit across injector

What it means

The ECM has detected a zero-resistance condition (short circuit) in the electrical path for the cylinder 5 injector's spill valve, preventing correct fuel timing and delivery.