Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC Diagnosis Procedure
- INSPECTION START
Confirm the detected malfunction (A or B). Refer to DTC Description .
Which malfunction is detected?
A
GO TO 2
B
GO TO 7.
- CHECK GROUND CONNECTION
- Turn ignition switch OFF.
- Check ground connection E191. Refer to Ground Inspection Inspection .
Is the inspection result normal?
YES
GO TO 3.
NO
Repair or replace ground connection.
- CHECK HO2S2 GROUND CIRCUIT
- Disconnect heated oxygen sensor 2 (HO2S2) harness connector.
- Disconnect ECM harness connector.
- Check the continuity between HO2S2 harness connector and ECM harness connector.
HO2S2
ECM
Continuity
Bank
Connector
Terminal
Connector
Terminal
1
F125
4
F143
81
Existed
- Also check harness for short to power.
Is the inspection result normal?
YES
GO TO 4.
NO
Repair open circuit, short to ground or short to power in harness or connectors.
- CHECK HO2S2 INPUT SIGNAL CIRCUIT
- Check the continuity between HO2S2 harness connector and ECM harness connector.
HO2S2
ECM
Continuity
Bank
Connector
Terminal
Connector
Terminal
1
F125
3
F143
49
Existed
- Check the continuity between HO2S2 harness connector and ground, or ECM harness connector and ground.
HO2S2
--
Continuity
Bank
Connector
Terminal
1
F125
3
Ground
Not existed
ECM
--
Continuity
Bank
Connector
Terminal
1
F143
49
Ground
Not existed
- Also check harness for short to power.
Is the inspection result normal?
YES
GO TO 5.
NO
Repair open circuit, short to ground or short to power in harness or connectors.
- Check the continuity between HO2S2 harness connector and ECM harness connector.
- CHECK HO2S2 CONNECTOR FOR WATER
Check connectors for water.
Water should not exist.
Is the inspection result normal?
YES
GO TO 6.
NO
Repair or replace harness or connectors.
- CHECK HEATED OXYGEN SENSOR 2
Refer to Component Inspection .
Is the inspection result normal?
YES
INSPECTION END
NO
Replace malfunctioning heated oxygen sensor 2. Refer to CATALYST : Exploded View .
- CHECK GROUND CONNECTION
- Turn ignition switch OFF.
- Check ground connection E191. Refer to Ground Inspection Inspection .
Is the inspection result normal?
YES
GO TO 8.
NO
Repair or replace ground connection.
- CLEAR THE MIXTURE RATIO SELF-LEARNING VALUE
- Clear the mixture ratio self-learning value. Refer to Work Procedure .
- Run engine for at least 10 minutes at idle speed.
Is the 1st trip DTC P0172 detected? Is it difficult to start engine?
YES
Perform trouble diagnosis for DTC P0172. Refer to DTC Description .
NO
GO TO 9.
- CHECK HO2S2 GROUND CIRCUIT
- Turn ignition switch OFF.
- Disconnect heated oxygen sensor 2 harness connector.
- Disconnect ECM harness connector.
- Check the continuity between HO2S2 harness connector and ECM harness connector.
HO2S2
ECM
Continuity
Bank
Connector
Terminal
Connector
Terminal
1
F125
4
F143
81
Existed
- Also check harness for short to power.
Is the inspection result normal?
YES
GO TO 10.
NO
Repair open circuit, short to ground or short to power in harness or connectors.
- CHECK HO2S2 INPUT SIGNAL CIRCUIT
- Check the continuity between HO2S2 harness connector and ECM harness connector.
HO2S2
ECM
Continuity
Bank
Connector
Terminal
Connector
Terminal
1
F125
3
F143
49
Existed
- Check the continuity between HO2S2 harness connector or ECM harness connector and ground.
HO2S2
--
Continuity
Bank
Connector
Terminal
1
F125
3
Ground
Not existed
ECM
--
Continuity
Bank
Connector
Terminal
1
F143
49
Ground
Not existed
- Also check harness for short to power.
Is the inspection result normal?
YES
GO TO 11.
NO
Repair open circuit, short to ground or short to power in harness or connectors.
- Check the continuity between HO2S2 harness connector and ECM harness connector.
- CHECK HEATED OXYGEN SENSOR 2
Refer to Component Inspection .
Is the inspection result normal?
YES
INSPECTION END
NO
Replace malfunctioning heated oxygen sensor 2. Refer to CATALYST : Exploded View .
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.