What causes a P104D code?

P104D 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 P104D code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P104D 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.

OBD-II

P104D

APSPD P3 (exhaust air pressure before turbine) sensor plausibility fault (high threshold)

What it means

The Engine Control Module (ECM) has detected that the Exhaust Back Pressure (P3) sensor reading is higher than expected relative to other pressure sensors (like boost or barometric) during specific engine operating conditions, indicating a plausibility error.