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.

CAUTION: After servicing or replacing faulty parts, perform Clear Memory Mode Ref. to ENGINE (DIAGNOSTICS) (H4DO) > Clear Memory Mode > OPERATION , and Inspection Mode Ref. to ENGINE (DIAGNOSTICS) (H4DO) > Inspection Mode > PROCEDURE .

WIRING DIAGRAM:

Engine Electrical System NON-TURBO MODEL (WITHOUT PUSH BUTTON START) Ref. to WIRING SYSTEM > Engine Electrical System > NON-TURBO MODEL (WITHOUT PUSH BUTTON START) .
Engine Electrical System NON-TURBO MODEL (WITH PUSH BUTTON START) Ref. to WIRING SYSTEM > Engine Electrical System > NON-TURBO MODEL (WITH PUSH BUTTON START) .

Fig 1: Engine Electrical System Non-Turbo Model Wiring Diagram

Courtesy of SUBARU OF AMERICA, INC.

CHECK REAR OXYGEN SENSOR CONNECTOR AND COUPLING CONNECTOR .
Has water entered the connector?

Yes: Completely remove any water inside.

No: Go to 2 .
CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR .
1. Turn the ignition switch to OFF.
2. Disconnect the connector from ECM and rear oxygen sensor.
3. Measure the resistance of harness between ECM connector and rear oxygen sensor connector.
  Connector & terminal
  
  (B136) No. 21 - (E25) No. 3:
  
  (B135) No. 30 - (E25) No. 4:
Is the resistance less than 1 Ω?

Yes: Go to 3 .

No: Repair the harness and connector.
NOTE:
In this case, repair the following item:
- Open circuit in harness between ECM connector and rear oxygen sensor connector
- Poor contact of coupling connector
CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR .
Measure the resistance between ECM connector and chassis ground.

Connector & terminal

(B136) No. 21 - 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.
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
- Loose part and improper installation 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 .