What causes a P0126 code?

P0126 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 P0126 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0126 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

P0126

P0126 Insufficient Coolant Temperature for Stable Operation

What it means

The Engine Control Module (ECM) detects that the coolant temperature has failed to reach the required operating threshold within a specific timeframe after engine start.