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

Fig 1: HO2S Heater Control Low (Bank 1 Sensor 2) - Wiring Diagram

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE

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  (B136) No. 20 - (E25) No. 3:	Is the resistance less than 1 Ω?	Go to step 2  .	Repair the harness and connector. NOTE: In this case, repair the following item: Open circuit in harness between ECM and rear oxygen sensor connector Poor contact of coupling connector
2 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR  . Measure the resistance between rear oxygen sensor connector and chassis ground. Connector & terminal  (E25) 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 DTC is detected, 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, temporary open or short circuit of harness may be the cause.