Engine General Information and Diagnosis: 1A-138
DTC P0420: Catalyst System Efficiency below Threshold
S5JB0A1104044
System and Wiring Diagram
Circuit Description
ECM monitors oxygen concentration in the exhaust gas which has passed the warm up three way catalytic converter
by HO2S-2. When the catalyst is functioning properly, the variation cycle of HO2S-2 output voltage (oxygen
concentration) is slower than that of A/F sensor output signal because of the amount of oxygen in the exhaust gas
which has been stored in warm up three way catalytic converter.
A/F Sensor Description
Refer to “A/F Sensor Description: ”.
DTC Detecting Condition and Trouble Area
C37-11
C37-38
C37-57
WHT
BRN
1
3
2
4
5 V
YEL
BLUWHTBLU WHT
C37-37
BLK
5
5 V
I5JB0A110053-02
1. A/F sensor 3. Warm up three way catalytic converter 5. ECM
2. HO2S-2 4. Three way catalytic converter
DTC detecting condition Trouble area
Ratio of integrated value of HO2S-2 output variation per integrated
value of A/F sensor output variation is more than specification while
vehicle is running constant speed and low engine load after warmed
up.
(*2 driving cycle detection logic, monitoring once / 1 driving)
• Exhaust gas leak
• Warm up three way catalytic converter
malfunction
• HO2S-2 malfunction
• A/F sensor malfunction
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