Suzuki SY413 Service Manual page 2684

DTC P0420
INSPECTION
STEP
1 Was "ENGINE DIAG. FLOW TABLE" performed?
2 Check Short Term Fuel Trim.
Did short term fuel trim vary within – 20% – +20%
range in step 3) of DTC confirmation test?
3 Check HO2S-2 for Output Voltage.
Perform steps 1) through 9) of DTC confirmation
procedure for DTC P0136 (HO2S-2 malfunction)
and check output voltage of HO2S-2 then.
Is over 0.6 V and below 0.3 V indicated?
ENGINE GENERAL INFORMATION AND DIAGNOSIS (G13/G16 ENGINE WITH WU TWC) 6-1-85
ACTION YES
Go to Step 2.
Go to Step 3.
Replace three way cata-
lytic converter.
NO
Go to "ENGINE DIAG.
FLOW TABLE".
Check fuel system.
Go to DTC P0171/P0172
Diag. Flow Table.
Check "Bl" and "P" wires
for open and short, and
connections for poor
connection.
If wires and connections
are OK, replace
HO2S-2.