DTC P2271: O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2: Notes

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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.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE CHECK BOARD .

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

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 .
CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR (OPEN) .
1. Turn the ignition switch to OFF.
2. Disconnect the connector from ECM.
3. Disconnect the connector from the rear oxygen sensor.
4. Measure the resistance of harness between ECM connector and rear oxygen sensor connector.
  Connector & terminal
  
  (B134) No. 33 - (B19) No. 3:
  
  (B134) No. 44 - (B19) 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.
CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR (SHORT TO GROUND) .
Measure the resistance between the ECM connector and engine ground.

Connector & terminal

(B134) No. 33 - 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.
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 .