What causes a P0666 code?

P0666 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 P0666 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0666 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

P0666

PCM/ECM/TCM Internal Temperature Sensor Circuit Fault

What it means

The engine control module or transmission control module has detected an out-of-range signal or circuit failure for its internal temperature sensor.