DTC P2271 O2 Sensor Signal Biased/Stuck Rich (Bank 1 Sensor 2): Wiring Diagram

Engine Electrical System ENGINE TYPE FB (WITHOUT PUSH BUTTON START) <Ref. to ENGINE PERFORMANCE (Legacy), ENGINE PERFORMANCE (Outback), Engine Electrical System.>
Engine Electrical System ENGINE TYPE FB (WITH PUSH BUTTON START) <Ref. to ENGINE PERFORMANCE (Legacy), ENGINE PERFORMANCE (Outback), Engine Electrical System.>

Fig 1: O2 Sensor Signal Biased/Stuck Rich (Bank 1 Sensor 2) - Wiring Diagram
Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTICS PROCEDURE

Step	Check	Yes	No
1 CHECK REAR OXYGEN SENSOR CONNECTOR.	Has water entered the connector?	Completely remove any water inside.	Go to step 2 .
2 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR. Turn the ignition switch to OFF. Disconnect the connector from ECM and rear oxygen sensor. Measure the resistance of harness between ECM connector and rear oxygen sensor connector. Connector & terminal (E158) No. 56 - (E25) No. 4: (E158) No. 57 - (E25) No. 3:	Is the resistance less than 1 Ω?	Go to step 3 .	Repair the open circuit of harness between ECM connector and rear oxygen sensor connector.
3 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR. Measure the resistance between the ECM connector and engine ground. Connector & terminal (E158) No. 56 - Engine ground:	Is the resistance 1 MΩ or more?	Go to step 4 .	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?	Repair or replace faulty parts.	Replace the rear oxygen sensor. <Ref. to REAR OXYGEN SENSOR .>