Circuit Description

WARNING: This page is about a different car, the 2002 Pontiac Sunfire and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

When the vehicle is first started, the engine operates in an Open Loop operation, ignoring the Oxygen Sensor (O2S) signal and calculating the air/fuel ratio based on inputs from the Engine Coolant Temperature (ECT), Throttle Position (TP), and Manifold Absolute Pressure (MAP) sensors only. The PCM will begin by using the Oxygen Sensor (O2S) signal for controlling the fuel delivery, closed loop, when the following conditions are met:

The engine has run a minimum amount of time based on ECT at engine start up.
The O2S 1 has a varying voltage output showing that the sensor is hot enough to operate properly.
The ECT has increased a minimum amount based on the ECT at engine start up.