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

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.>.
Use the check board when measuring the ECM terminal voltage and resistance.

WIRING DIAGRAM:

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

Fig 1: A/F/O2 Heater Control Circuit Low Bank 1 Sensor 1 - 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 (E24) No. 3 (+) - 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 in harness between A/F, oxygen sensor relay and front oxygen (A/F) sensor connector Poor contact of A/F, oxygen sensor relay connector Poor contact of coupling connector Malfunction of A/F, oxygen sensor relay
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 (E24) No. 2 - (E159) No. 9:	Is the resistance less than 1 Ω?	Go to step 3 .	Repair the open circuit of harness between ECM connector and front oxygen (A/F) sensor connector.
3 CHECK GROUND CIRCUIT FOR ECM. Measure the resistance of harness between ECM connector and engine ground. Connector & terminal (B134) No. 35 - Engine ground: (B134) No. 47 - Engine ground: (E159) No. 10 - Engine ground: (E159) No. 17 - Engine ground: (E159) No. 18 - Engine ground: (E159) No. 25 - Engine ground: (E159) No. 26 - Engine ground:	Is the resistance less than 5 Ω?	Go to step 4 .	Repair the harness and connector. NOTE: In this case, repair the following item: Open circuit of harness between ECM connector and engine ground Poor contact of coupling connector
4 CHECK FRONT OXYGEN (A/F) SENSOR. Measure the resistance between front oxygen (A/F) sensor terminals. Terminals No. 2 - No. 3:	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 .>