Dtc P0420 Catalyst System Efficiency Below Threshold (Bank 1) - Suzuki GRAND VITARA XL-7 Owner's Manual

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6-1-94 ENGINE GENERAL INFORMATION AND DIAGNOSIS (H27 ENGINE)

DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)

SYSTEM DIAGRAM

1. HO2S-1 (Bank-1)

2. HO2S-2 (Bank-1)

5. ECM (PCM)

CIRCUIT DESCRIPTION

Exhaust oxygen concentration at the pre-catalyst and the post-catalyst of WU-TWC is detected from HO2S-1

and HO2S-2 respectively and accordingly ECM (PCM) controls the closed loop which then controls the fuel

injection volume. (Refer to Section 6E2.) While the above control is going on and if WU-TWC is in good condi-

tion, the output voltage of HO2S-2 is maintained at specified level. As WU-TWC becomes deteriorated, even

when the above control is going on, the exhaust gas which has passed WU-TWC then passes HO2S-2 at the

exhaust oxygen concentration similar to that of the pre-catalyst without being oxygenated or converted. Thus,

waveforms of HO2S-1 and HO2S-2 output voltages become alike. ECM (PCM) judges deterioration of WU-TWC

by comparing waveforms of HO2S-1 and HO2S-2.

DTC DETECTING CONDITION AND TROUBLE AREA

DTC DETECTING CONDITION

While running under conditions described for DTC CON-

FIRMATION PROCEDURE, output waveform of HO2S-1

becomes similar to that of HO2S-2.

(2 driving cycle detection logic)

TROUBLE AREA

• Exhaust gas leakage

• Warm up three way catalytic converter

• Heated oxygen sensor – 2 or its circuit

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