What causes a SPN 3478 code?

SPN 3478 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 SPN 3478 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3478 active.

How do I fix SPN 3478?

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

J1939 SPN

SPN 3478

SPN 3478 FMI 2/7/12 Aftertreatment 1 Fuel Pressure Control Fault

What it means

Indicates a performance issue with the Hydrocarbon (HC) Doser unit specifically regarding fuel delivery or pressure regulation to the Diesel Oxidation Catalyst (DOC). This component is responsible for supplying diesel fuel for the regeneration process.