What causes a P1857 code?

P1857 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 P1857 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1857 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

P1857

Upstream NOx sensor NOx signal-related data out of range fault

What it means

The Engine Control Module (ECM) detects that the signal from the Inlet (Upstream) NOx sensor is physically impossible or inconsistent with the engine's current operating parameters.