What causes a P171C code?

P171C 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 P171C code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P171C 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

P171C

EGRRD NOx governor slow response increment

What it means

The Engine Control Module (ECM) has detected that the downstream (Outlet) NOx sensor is responding too slowly to changes in exhaust chemistry commanded by the NOx governor logic.