What causes a SPN 3304 code?

SPN 3304 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 3304 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3304 active.

How do I fix SPN 3304?

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 3304

SPN 3304 - DPF Regeneration Inhibited due to Inhibit Switch

What it means

The Engine Control Module detects that the Diesel Particulate Filter (DPF) regeneration is being prevented by a driver-controlled inhibit switch or a logic-based lockout.