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 (CROSSTREK MODEL)>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 (OPEN)  .
   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 

      (B134) No. 44 - (B19) No. 4:

      (B134) No. 33 - (B19) No. 3:

   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 (SHORT TO GROUND)  .

   Measure the resistance between the ECM connector and engine ground.

   Connector & terminal 

   (B134) No. 33 - Chassis 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) (H4DO)>REAR OXYGEN SENSOR .