The Heated Oxygen Sensor (HO2S) Monitor is an on-board strategy designed to monitor the HO2S sensors for a malfunction or deterioration that can affect emissions. Under specific conditions, the fuel control or upstream HO2S sensors are checked for proper output voltage and response rate (the time it takes to switch from lean to rich or rich to lean). Downstream HO2S sensors used for Catalyst Monitor are also monitored for proper output voltage. Input is required from the Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT), Inlet Air Temperature (IAT), Mass Air Flow (MAF), Throttle Position (TP) and Crankshaft Position (CKP) sensors to activate the HO2S Monitor. The Fuel System Monitor and Misfire Detection Monitor must also have completed successfully before the HO2S Monitor is enabled.
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