Monitor Description

The ECM monitors the rear heated oxygen sensor (HO2S) in the following 3 items:

1. The HO2S voltage changes between Rich (more than 0.45 volts) and Lean (less than 0.45 volts) while the vehicle is running (repeating acceleration and deceleration) for 8 minutes. If not, the ECM interprets this as a malfunction, illuminates the MIL, and then sets DTC.
2. The HO2S voltage does not remain at less than 0.05 volts for a long time while the vehicle is running (60 % of the time in the 220 second-monitor, the sensor output is less than 0.05 V). If it does, the ECM interprets this as a malfunction, illuminates the MIL, and then sets a DTC.
3. The sensor's voltage drops to below 0.2 volts (extremely Lean status) immediately when the vehicle decelerates and the fuel cut is working for 7 seconds. If not, the ECM interprets this to mean the sensor's response feature has deteriorated, illuminates the MIL, and then sets DTC.
4. The rear oxygen sensor impedance is 5 Ω. or less, 15 kQ. or more, or output voltage is 1.2 V or more (normal voltage: 0 to 1.0 V). If so, the ECM will determine that the rear oxygen sensor or a related circuit has an open or short circuit, illuminate the MIL and set a DTC.

Impedance is detected by the IC inside the ECM.