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 CHART

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)". <Ref. to 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 - (B18) No. 3:	Is the resistance less than 1 Ω?	Go to step 3.	Repair the harness and connector. NOTE: In this case, repair the following item: Open circuit in harness between rear oxygen sensor and ECM connector
3 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.  Measure the resistance between rear oxygen sensor harness connector and chassis ground. Connector & terminal  (B18) No. 3 - Chassis ground:	Is the resistance 1 MΩ or more?	Go to step 4.	Repair the chassis short circuit of the harness between the rear oxygen sensor and ECM connector.
4 CHECK REAR OXYGEN SENSOR.  Measure the resistance between rear oxygen sensor terminals. Terminals  No. 3 - No. 4:	Is the resistance less than 1 Ω?	Replace the rear oxygen sensor. <Ref. to REAR OXYGEN SENSOR . >	Repair the poor contact in rear oxygen sensor connector.