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 Schematics

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSIS 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 - (T6) 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 (T6) 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. Refer to REAR OXYGEN SENSOR .	Even if the malfunction indicator light illuminates, the circuit has returned to a normal condition at this time. Reproduce the fault condition, and reperform the check. NOTE: In this case, there may be a temporary connector contact failure.

Step

Check

Yes

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 - (T6) 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

(T6) 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. Refer to REAR OXYGEN SENSOR .

Even if the malfunction indicator light illuminates, the circuit has returned to a normal condition at this time. Reproduce the fault condition, and reperform the check.

NOTE: In this case, there may be a temporary connector contact failure.