Circuit/System Description

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The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during open loop and closed loop. During open loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During closed loop, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0%. If the HO2S indicates a rich condition, the fuel trim values will be below 0%. The short term fuel trim values change rapidly in response to the HO2S voltage signals. The long term fuel trim makes rough adjustments in order to maintain an optimal air/fuel ratio. A block of memory cells contain information arranged in combinations of engine speed and engine load for a full range of vehicle operating conditions. The long term fuel trim diagnostic is based on an average of cells currently being used. The ECM selects the cells based on engine speed and load. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if more vapor than the customer may desire from the evaporative emission (EVAP) canister is causing a rich condition.

The heating elements inside each heated oxygen sensor (HO2S) heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter closed loop earlier and the control module to calculate the air-to-fuel ratio sooner.

The heated oxygen sensor (HO2S) utilizes the following circuits:

A signal circuit
A low reference circuit
An ignition voltage circuit
A heater control circuit