DTC P0139 O2 Sensor Circuit Slow Response (Bank 1 Sensor 2): Wiring Diagram

Fig 1: O2 Sensor Circuit Slow Response (Bank 1 Sensor 2) - Wiring Diagram

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSIS PROCEDURE

Step	Check	Yes	No
1 CHECK ANY OTHER DTC ON DISPLAY.	Is any other DTC displayed?	Check DTC using LIST OF DIAGNOSTIC TROUBLE CODE (DTC) . NOTE: In this case, it is not necessary to inspect DTC P0139.	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 and rear oxygen sensor connector. Connector & terminal  (B135) No. 4 - (E61) No. 3:	Is the resistance less than 1 Ω?	Go to step 3  .	Repair the open circuit of harness between ECM and rear oxygen sensor connector.
3 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.  Measure the resistance between rear oxygen sensor connector and chassis ground. Connector & terminal  (E61) No. 3 - Chassis ground	Is the resistance 1 MΩ or more?	Go to step 4  .	Repair the ground short circuit of harness.
4 CHECK REAR OXYGEN SENSOR.  Measure the resistance between connector terminals of rear oxygen sensor. Terminals  No. 3 - No. 4	Is the resistance less than 1 Ω?	Replace the rear oxygen sensor. <Ref. to REAR OXYGEN SENSOR . >	Temporary poor contact occurs. Check for poor contact of connectors.