1A-90 Engine General Information and Diagnosis:
4 HO2S-1 ground check
1) Disconnect connector from HO2S-1 with ignition switch
turned OFF.
2) Check for proper connection to HO2S-1 connector at
“BLK/RED”, “WHT”, “BLK/WHT” and “YEL” wire
terminals.
3) If connections are OK, measure resistance between
“YEL” wire terminal of HO2S-1 connector and engine
ground.
Is measured resistance less than 5
Ω
?
Go to Step 5. “YEL” wire is open or
high resistance circuit.
Poor “C37-57” terminal
connection. Faulty ECM
ground.
If they are OK,
substitute a known-
good ECM and recheck.
5 Wire circuit check
1) Turn OFF ignition switch.
2) Remove ECM from its bracket with ECM connectors
connected.
3) Measure resistance between “WHT” wire terminal of
HO2S-1 connector and “C37-10” terminal of ECM
connector.
Is resistance less than 5
Ω
?
Go to Step 6. “WHT” wire is high
resistance circuit or
open circuit. Poor “C37-
10” terminal connection.
Faulty ECM ground. If
they are OK, substitute
a known-good ECM and
recheck.
6 Wire circuit check
1) Disconnect connectors from ECM with ignition switch
turn OFF.
2) Measure resistance between “WHT” wire terminal of
HO2S-1 connector and vehicle body ground.
Is resistance infinity?
Go to Step 7. “WHT” wire is shorted to
ground circuit.
7 HO2S-1 signal circuit check
1) Measure voltage between “WHT” wire terminal of HO2S-
1 connector and vehicle body ground.
Is voltage 0 V?
Go to Step 8. “WHT” wire is shorted to
other circuit.
8 HO2S-1 heater circuit check
1) Check HO2S-1 heater circuit referring to “DTC P0031 /
P0032: HO2S Heater Control Circuit Low / High
(Sensor-1)”.
Is circuit in good condition?
Go to Step 9. Repair HO2S-1 circuit.
9 Exhaust system check
1) Check exhaust system for exhaust gas leakage.
Is it OK?
Go to Step 4 in “DTC
P0171 / P0172: Fuel
System Too Lean /
Rich”.
If it is in good condition,
go to Step 10.
Repair leakage of
exhaust system.
10 Air intake system check
1) Check air intake system for clog or leak.
Is it OK?
Check HO2S-1 referring
to “HO2S-1 and HO2S-
2 Heater On-Vehicle
Inspection in Section
1C”.
If it is in good condition,
substitute a known-
good ECM and recheck.
Repair or replace air
intake system.
Step Action Yes No
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