Circuit Description

An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.

The airflow into the engine is accumulated and used to determine if the vehicle has been driven within conditions that would allow the engine coolant to heat up normally to the Closed Loop temperature. If the coolant temperature does not increase normally or does not reach the Closed Loop temperature, the diagnostics that use ECT as enabling criteria may not run when expected.

If the PCM detects the calibrated amount of airflow and engine run time has been met and the engine coolant has not met the Closed Loop temperature, DTC P0125 sets.