DTC P0031: A/F/O2 Heater Control Circuit Low Bank 1 Sensor 1: Notes

WARNING: This page is about a different variant/trim than selected.

DTC detecting condition:

Immediately at fault recognition

CAUTION: After servicing or replacing faulty parts, perform Clear Memory Mode Ref. to OPERATION , Clear Memory Mode and Inspection Mode Ref. to PROCEDURE , Inspection Mode.

Wiring diagram:

Engine Electrical System Ref. to WIRING DIAGRAM , Engine Electrical System.

Fig 1: Front Oxygen Sensor Wiring Diagram

Courtesy of SUBARU OF AMERICA, INC.

Step	Check	Yes	No
1 CHECK POWER SUPPLY TO FRONT OXYGEN (A/F) SENSOR. Turn the ignition switch to OFF. Disconnect the connectors from front oxygen (A/F) sensor. Turn the ignition switch to ON. Measure the voltage between front oxygen (A/F) sensor connector and engine ground. Connector & terminal (E47) No. 2 (+) - Engine ground (-):	Is the voltage 10 V or more?	Go to step 2	Repair the power supply line. NOTE: In this case, repair the following item: Open circuit of harness between M/B main relay and front oxygen (A/F) sensor connector Poor contact of M/B main relay connector Poor contact of coupling connector Defective M/B main relay Blown out of fuse (M/B No. 20)
2 CHECK HARNESS BETWEEN ECM AND FRONT OXYGEN (A/F) SENSOR CONNECTOR. Turn the ignition switch to OFF. Disconnect the connector from ECM. Measure the resistance between ECM connector and front oxygen (A/F) sensor connector. Connector & terminal (E158) No. 5 - (E47) No. 1:	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 ECM connector and front oxygen (A/F) sensor connector Poor contact of coupling connector
3 CHECK GROUND CIRCUIT FOR ECM. Measure the resistance of harness between ECM connector and chassis ground. Connector & terminal (E158) No. 60 - Chassis ground: (E158) No. 61 - Chassis ground: (E158) No. 62 - Chassis ground: (E158) No. 63 - Chassis ground: (E158) No. 64 - Chassis ground: (E158) No. 65 - Chassis ground:	Is the resistance less than 5 Ω?	Go to step 4	Repair the open circuit in harness between ECM connector and engine ground.
4 CHECK FRONT OXYGEN (A/F) SENSOR. Measure the resistance between front oxygen (A/F) sensor connector terminals. Terminals No. 2 - No. 1:	Is the resistance 2 - 3 Ω?	Repair the poor contact of ECM connector.	Replace the front oxygen (A/F) sensor. Ref. to FRONT OXYGEN (A/F) SENSOR