Circuit Description

An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the engine control module (ECM) for engine control and as an enabling criteria for other diagnostics. This input also determines if the ECT is insufficient for Closed Loop fuel control.

This time to Closed Loop fuel control diagnostic is designed to detect a system that is not reaching optimum fuel control in a reasonable amount of time. When the engine is started, the ECM uses a timer and a modeled ECT table that is based on ECT at start-up to determine a calibrated threshold. When this threshold is met, the modeled ECT is compared to the actual measured ECT.

If the ECM detects that the measured ECT is not within a calibrated range of the modeled ECT, DTC P0125 sets.