What causes a P2251 code?

P2251 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 P2251 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P2251 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

P2251

O2 Sensor Negative Current Control Circuit Open Bank 1 Sensor 1

What it means

The Engine Control Module (ECM) has detected an open circuit in the reference ground or negative current control circuit for the upstream oxygen sensor. This sensor is critical for closed-loop air-fuel ratio monitoring.