What causes a P1266 code?

P1266 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 P1266 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1266 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

P1266

Increase in combustion in cylinder 2 relative to the others.

What it means

The ECM has detected that cylinder 2 is contributing significantly more power/torque than the other cylinders via the crankshaft position sensor speed fluctuations.