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 P2270: O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 2: Notes
DTC detecting condition:
Detected when two consecutive driving cycles with fault occur.
- After servicing or replacing faulty parts, perform Clear Memory Mode. Refer to ENGINE (DIAGNOSTICS) (W/O STI)>CLEAR MEMORY MODE>OPERATION ., and inspection mode. Refer to ENGINE (DIAGNOSTICS) (W/O STI)>INSPECTION MODE>PROCEDURE .
- Use the check board when measuring the ECM terminal voltage and resistance.
Wiring diagram:
Engine Electrical System. Refer to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .
- CHECK REAR OXYGEN SENSOR CONNECTOR.
Check the rear oxygen sensor connector.
Has water entered the connector?
Yes: Completely remove any water inside.
No: Go to 2.
- CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.
- Turn the ignition switch to OFF.
- Disconnect the connector from ECM.
- Disconnect the connector from rear oxygen sensor.
- Measure the resistance of harness between ECM connector and rear oxygen sensor connector.
Connector & terminal
(E158) No. 42 - (E25) No. 3:
(E158) No. 16 - (E25) No. 4:
Is the resistance less than 1 Ω?
Yes: Go to 3.
No: Repair the open circuit of harness between ECM connector and rear oxygen sensor connector.
- CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.
- Connect the connector to ECM.
- Turn the ignition switch to ON.
- Measure the voltage between rear oxygen sensor connector and engine ground.
Connector & terminal
(E25) No. 3 (+) - Engine ground (-):
Is the voltage 0.15 V or more?
Yes: Repair the short circuit to power in the harness between ECM connector and rear oxygen sensor connector.
No: Go to 4.
- CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE: Check the following items.- Looseness and improper fitting of exhaust system parts
- Damage (crack, hole etc.) of parts
- Damage (crack, hole etc.) between front oxygen (A/F) sensor and rear oxygen sensor
Is there any fault in exhaust system?
Yes: Repair or replace faulty parts.
No: Replace the rear oxygen sensor. Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>REAR OXYGEN SENSOR .
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.