What causes a P1515 code?

P1515 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 P1515 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1515 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

P1515

DEFOI EGR system category fault

What it means

DEFOI EGR System Category Fault: This is a logic-based code indicating the engine control module has detected that the EGR system and the DEF/SCR system are not working in tandem to sufficiently reduce emissions to required levels.