Circuit Description

When the vehicle is first started, it operates in Open Loop, ignoring the oxygen sensor (O2S) signal and calculating the fuel/air ratio based on inputs from the Engine Coolant Temperature (ECT), throttle position (TP) and manifold absolute pressure (MAP) sensors only. The engine control module (ECM) will begin using the O2S signal for controlling 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 has a varying voltage output showing that it is hot enough to operate properly.
• The ECT has increased a minimum amount based on ECT at engine start up.