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.

DIAGNOSTIC PROCEDURE CHART

Step	Check	Yes	No
1 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 - (E23) No. 3:	Is the resistance less than 1 Ω?	Go to step 2.	Repair the open circuit of harness between ECM and rear oxygen sensor connector.
2 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.  Measure the resistance between rear oxygen sensor connector and chassis ground. Connector & terminal  (E23) No. 3 - Chassis ground:	Is the resistance 1 MΩ or more?	Go to step 3.	Repair the ground short circuit of harness between ECM and rear oxygen sensor connector.
3 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 . >	Even if the malfunction indicator light illuminates, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again. NOTE: In this case, temporary poor contact of connector may be the cause.