DTC P2271: O2 Sensor Signal Biased/Stuck Rich 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 .

Courtesy of SUBARU OF AMERICA, INC.

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

      Connector and terminal. 

      (E158) No. 30 - (E25) No. 3:

      (E158) No. 31 - (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.

3. CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR (SHORT TO GROUND). 

   Measure the resistance between the ECM connector and engine ground.

   Connector and terminal. 

   (E158) No. 31 - Engine ground:

   Is the resistance 1 MΩ or more?

   Yes  : Go to  4.

   No  : Repair the short circuit to ground in harness between ECM connector and rear oxygen sensor connector.

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) (H4DOTC)>REAR OXYGEN SENSOR .