Monitor Description

WARNING: This page is about a different variant/trim than selected.

The ECM (included in hybrid vehicle control ECU) uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency.

The first sensor, the Air-Fuel Ratio (A/F) sensor, sends pre-catalyst information to the ECM.

The second sensor, the Heated Oxygen (HO2) sensor, sends post-catalyst information to the ECM. In order to detect any deterioration in the TWC, the ECM calculates the Oxygen Storage Capacity (OSC) of the TWC. This calculation is based on the voltage output of the HO2 sensor while performing active air-fuel ratio control, rather than the conventional detecting method, which uses the locus ratio.

The OSC value is an indication of the oxygen storage capacity of the TWC. When the vehicle is being driven with a warm engine, active air-fuel ratio control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the air-fuel ratio to lean or rich levels. If the cycle of the waveform for the HO2 sensor is long, the OSC great. There is a direct correlation between the HO2 sensor and the OSC of the TWC.

The ECM uses the OSC value to determine the state of the TWC. If any deterioration has occurred, it illuminates the MIL and sets the DTC.

DTC TROUBLE DETECTION CONDITION CHART

DTC No.	DTC Detection Conditions	Trouble Areas
P0420	OSC value smaller than standard value under active air-fuel ratio control (2-trip detection logic)	Front exhaust pipe (with TWC) Gas leakage from exhaust system Air-Fuel Ratio (A/F) sensor (sensor 1) Heated Oxygen (HO2) sensor (sensor 2)