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.

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM>Engine Electrical System>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. 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

2. CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from ECM.
   3. Disconnect the connector from rear oxygen sensor.
   4. Measure the resistance of harness between ECM connector and rear oxygen sensor connector.

      Connector & terminal 

      (B136) No. 20 - (T6) No. 3:

      (B135) No. 30 - (T6) No. 4:

   Is the resistance less than 1 Ω?

   Yes:  Go to  3

   No:  Repair the harness and connector.

   NOTE: In this case, repair the following item:

   • Open circuit in harness between ECM connector and rear oxygen sensor connector
   • Poor contact of coupling connector
3. CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR  .
   1. Connect the connector to ECM.
   2. Turn the ignition switch to ON.
   3. Measure the voltage between rear oxygen sensor connector and chassis ground.

      Connector & terminal 

      (T6) No. 4 (+) - Chassis 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

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. Ref. to FUEL INJECTION (FUEL SYSTEMS) (STI)>Rear Oxygen Sensor .