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.
Diagnosis Procedure
- CHECK GROUND CONNECTION
- Turn ignition switch OFF.
- Check ground connection E24. Refer to Ground Inspection in Circuit Inspection .
Is the inspection result normal?
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GO TO 2.
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Repair or replace ground connection.
- RETIGHTEN A/F SENSOR 1 AND HEATED OXYGEN SENSOR 2
- Loosen and retighten the A/F sensor 1 and heated oxygen sensor 2. Refer to Removal and Installation (A/F sensor 1) and Removal and Installation (Heated oxygen sensor 2).
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GO TO 3.
- CHECK FOR EXHAUST GAS LEAK
- Start engine and run it at idle.
- Listen for an exhaust gas leak before the three way catalyst 2.
Is exhaust gas detected?
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Repair or replace.
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GO TO 4.
- CHECK FOR INTAKE AIR LEAK
- Start engine and run it at idle.
- Listen for an intake air leak after the mass air flow sensor.
Is intake air leak detected?
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Repair or replace.
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GO TO 5.
- CLEAR THE MIXTURE RATIO SELF-LEARNING VALUE
- Clear the mixture ratio self-learning value. Refer to Description .
- Run engine for at least 10 minutes at idle speed.
Is the 1st trip DTC P0171 or P0172 detected? Is it difficult to start engine?
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Perform trouble diagnosis for DTC P0171 or P0172.
- P0171: DTC Description .
- P0172: DTC Description .
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GO TO 6.
- CHECK HARNESS CONNECTOR
- Turn ignition switch OFF.
- Disconnect A/F sensor 1 harness connector.
- Check harness connector for water.
Water should not exit.
Is the inspection result normal?
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GO TO 7.
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Repair or replace harness connector.
- CHECK A/F SENSOR 1 POWER SUPPLY
- Turn ignition switch ON.
- Check the voltage between A/F sensor 1 harness connector and ground.
+ - Voltage A/F sensor 1 Connector Terminal F68 4 Ground Battery voltage
Is the inspection result normal?
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GO TO 9.
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GO TO 8.
- CHECK A/F SENSOR 1 POWER SUPPLY CIRCUIT
- Turn ignition switch ON.
- Check the voltage between A/F sensor 1 harness connector and IPDM E/R harness connector.
A/F sensor 1 IPDM E/R Continuity Connector Terminal Connector Terminal F68 4 E121 26 Existed - Also check harness for short to ground.
Is the inspection result normal?
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Perform the trouble diagnosis for power supply circuit.
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Repair or replace error-detected parts.
- CHECK A/F SENSOR 1 INPUT SIGNAL CIRCUIT
- Turn ignition switch OFF.
- Disconnect ECM harness connector.
- Check the continuity between A/F sensor 1 harness connector and ECM harness connector.
A/F sensor 1 ECM Continuity Connector Terminal Connector Terminal F68 2 F79 102 Existed - Check the continuity between A/F sensor 1 harness connector and ground, or ECM harness connector and ground.
A/F sensor 1 - Continuity Connector Terminal F68 2 Ground Not existed ECM - Continuity Connector Terminal F79 102 Ground Not existed - Also check harness for short to power.
Is the inspection result normal?
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GO TO 10.
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Repair open circuit, short to ground or short to power in harness or connectors.
- CHECK A/F SENSOR 1 HEATER
Refer to Component Inspection (A/F Sensor 1 Heater) .
Is the inspection result normal?
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GO TO 11.
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GO TO 13.
- CHECK HEATED OXYGEN SENSOR 2
Refer to Component Inspection .
Is the inspection result normal?
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GO TO 12.
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Replace malfunctioning heated oxygen sensor 2. Refer to Removal and Installation .
- CHECK INTERMITTENT INCIDENT
Perform Intermittent Incident .
Is the inspection result normal?
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GO TO 13.
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Repair or replace.
- REPLACE AIR FUEL RATIO (A/F) SENSOR 1
Replace air fuel ratio (A/F) sensor 1. Refer to Removal and Installation .
Do you have CONSULT '
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GO TO 14.
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GO TO 15.
- CONFIRM A/F ADJUSTMENT DATA
With CONSULT
- Turn ignition switch ON.
- On CONSULT screen, select "ENGINE">>"Data Monitor">>"A/F ADJ-B1" and "A/F ADJ-B2".
- Make sure that "0.000" is displayed on CONSULT screen.
Is "0.000" displayed?
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INSPECTION END
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GO TO 15.
- CLEAR THE MIXTURE RATIO SELF-LEARNING VALUE
Clear the mixture ratio self-learning value. Refer to Description .
Do you have CONSULT '
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GO TO 16.
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INSPECTION END
- CONFIRM A/F ADJUSTMENT DATA
With CONSULT
- Turn ignition switch ON.
- On CONSULT screen, select "ENGINE">>"Data Monitor">>"A/F ADJ-B1" and "A/F ADJ-B2".
- Make sure that "0.000" is displayed on CONSULT screen.
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INSPECTION END
NO RELATED
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.