What causes a P171B code?

P171B 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 P171B code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P171B 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

P171B

EGRRD NOx governor slow response decrement

What it means

P171B indicates that the NOx reduction rate (governor) is responding too slowly when attempting to decrease emissions levels, specifically during the 'decrement' phase of dosage adjustment.