Suzuki SY413 Service Manual page 2682

DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD
CIRCUIT DESCRIPTION
Heated
oxygen
sensor-1
Warm up three way
catalytic converter
ECM (PCM) monitors oxygen concentration in the exhaust gas which has passed the 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 HO2S-1 output voltage because of the amount of oxygen in the exhaust gas which has been
stored in the catalyst.
Reference
Oscilloscope Waveforms
DTC DETECTING CONDITION
D While vehicle running at constant speed under other
than high load.
D Time from rich or lean switching command is output
till HO2S-2 output voltage crosses 0.45 V is less than
specified value.
: 2 driving cycle detection logic, monitoring once / 1
driving.
ENGINE GENERAL INFORMATION AND DIAGNOSIS (G13/G16 ENGINE WITH WU TWC) 6-1-83
To Other sensor
Three way catalytic converter
0.5 V / Div
2 sec. / Div
Engine running at
Closed loop condition
Heated oxygen
sensor-2
Fuel
Idle after fuel cut
Cut
POSSIBLE CAUSE
D Exhaust gas leak
D Three way catalytic converter malfunction
D Fuel system malfunction
D HO2S-2 malfunction
D HO2S-1 malfunction
ECM
(PCM)