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DTC P0420 Catalyst System Efficiency Below Threshold
SYSTEM/WIRING DIAGRAM
1
3
CIRCUIT DESCRIPTION
ECM monitors oxygen concentration in the exhaust gas which has passed the three way catalytic converter by
HO2S–2 (2).
When the catalyst is functioning properly, the variation cycle of HO2S–2 (2) output voltage (oxygen concentra-
tion) is slower than that of HO2S–1 (1) output voltage because of the amount of oxygen in the exhaust gas
which has been stored in warm up three way catalytic converter (3) and three way catalytic converter (4).
REFERENCE
[A]: Oscilloscope Waveforms
ORN
2
ENGINE GENERAL INFORMATION AND DIAGNOSIS 6-129
WHT
C63-11
ORN
C63-28
BRN
C63-33
4
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