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 & terminal 

      (E51) No. 4 - (E77) No. 3:

      (E51) No. 5 - (E77) 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 & terminal 

   (E51) No. 5 - 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.) of front oxygen (A/F) sensor or 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 .