DTC P0125 Insufficient Coolant Temperature For Closed Loop Fuel Control: General Description

When the engine is first started, the fuel control system operates in an open loop operation, ignoring the HO2S (Heated Oxygen Sensor) signal and calculating the air/fuel ratio based on inputs from the engine coolant temperature, the throttle position and the mass air flow sensors. The PCM will begin by using the oxygen sensor signal for controlling the fuel delivery (closed loop) when the following conditions are met:

• The engine has run a minimum amount of time at engine start up.
• The HO2S has a varying voltage output showing that it is hot enough to operate properly.
• The ECT has increased a minimum amount based on the ECT at start up.

The PCM monitors the amount of time for the cooling system to achieve closed loop operating temperature. The engine coolant temperature sufficient to allow closed loop operation is not achieved within a predetermined time frame, PCM sets DTC.