What causes a P1139 code?

P1139 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 P1139 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1139 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

P1139

WRAF heater calibration test fault

What it means

The ECM carries out a specific test to measure the resistance and power consumption of the WRAF sensor heater during startup. If the measured value falls outside of the narrow calibration window, this fault is triggered.