Circuit Description

When vehicle is first started, it operates in Open Loop, ignoring Oxygen Sensor (O2S1) signal and calculating fuel/air ratio based on inputs from Engine Coolant Temperature (ECT), Throttle Position (TP), and Manifold Absolute Pressure (MAP) sensors only. The powertrain control module (PCM)/engine control module (ECM) will begin using O2S1 signal for controlling fuel delivery (Closed Loop) when following conditions are met:

• The engine has run a minimum amount of time based on ECT at engine start up.
• The O2S1 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.