What causes a P0408 code?

P0408 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 P0408 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0408 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

P0408

Exhaust Gas Recirculation Sensor B Circuit High

What it means

The Engine Control Module (ECM) has detected a high voltage signal from the Exhaust Gas Recirculation (EGR) position sensor 'B' circuit, indicating a potential short to power or a failed sensor.