Circuit Description

When engine is first started, engine fuel control system operates in open loop. Air/fuel ratio is determined by inputs from Engine Coolant Temperature (ECT), Throttle Position (TP) and Manifold Absolute Pressure (MAP) sensors. PCM will begin using input from both HO2S to control fuel delivery (closed loop operation) when engine obtains normal operating temperature.

When DTC sets, MIL will illuminate after 2 consecutive ignition cycles in which diagnostic runs with active fault. PCM will record operating conditions at time of failure and store information in FREEZE FRAME/FAILURE RECORDS data buffer.