Suzuki 2000 Grand Vitara SQ416, Service Manual

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YH4
GRAND
VITARA
6-1-98 ENGINE (H25 ENGINE)
TERMINAL ARRANGEMENT OF ECM (PCM) COUPLER (VIEWED FROM HARNESS SIDE)
1. Warm up TWC converter (Bank 2)
2. Warm up TWC converter (Bank 1)
3. TWC converter
4. HO2S (Bank 2, Sensor 2) 5. HO2S (Bank 2, Sensor 1)
6. HO2S (Bank 1, Sensor 1)
7. HO2S (Bank 1, Sensor 2)
DTC P0420 CATALYST SYSTEM (BANK-1) EFFICIENCY BELOW THRESHOLD
DTC P0430 CATALYST SYSTEM (BANK-2) EFFICIENCY BELOW THRESHOLD
SYSTEM/ WIRING DIAGRAM
SYSTEM DESCRIPTION
Exhaust oxygen concentration at the upper part and the lower part of 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.
While the above control is going on and if TWC is in good condition, the output voltage of HO2S-2 is maintained
at specified level. As TWC is in becomes deteriorated, even when the above control is going on, the exhaust gas
which has passed TWC then passes HO2S-2 at the exhaust oxygen concentration similar to that of the upper part
of TWC without being oxygenated or converted. Thus, waveforms of HO2S-1 and HO2S-2 output voltage become
alike. ECM (PCM) judges deterioration of TWC by comparing waveforms of HO2S-1 and HO2S-2.