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

Engine Electrical System ENGINE TYPE FA (WITHOUT PUSH BUTTON START) <Ref. to 2.0L TURBO (WITHOUT PUSH BUTTON START), WIRING DIAGRAM, Engine Electrical System.>
Engine Electrical System ENGINE TYPE FA (WITH PUSH BUTTON START) <Ref. to 2.0L TURBO (WITH PUSH BUTTON START), WIRING DIAGRAM, Engine Electrical System.>

Fig 1: O2 Sensor Signal Biased/Stuck Rich Circuit Diagram
Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC 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 E-150 No. 42 - (E25) No. 3: E-150 No. 16 - (E25) No. 4:	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 E-150 No. 42 - 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 .>