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 ENGINE (DIAGNOSTICS) (H6DO)>CLEAR MEMORY MODE>OPERATION ., and inspection mode Ref. to ENGINE (DIAGNOSTICS) (H6DO)>INSPECTION MODE>PROCEDURE .
Use the check board when measuring the ECM terminal voltage and resistance.

Wiring diagram:

Engine Electrical System Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

CHECK POWER SUPPLY TO FRONT OXYGEN (A/F) SENSOR.
1. Turn the ignition switch to OFF.
2. Disconnect the connectors from front oxygen (A/F) sensor.
3. Turn the ignition switch to ON.
4. 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?

Yes Go to 2 .

No 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)
CHECK HARNESS BETWEEN ECM AND FRONT OXYGEN (A/F) SENSOR CONNECTOR.
1. Turn the ignition switch to OFF.
2. Disconnect the connector from ECM.
3. 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?

Yes Go to 3 .

No 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
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?

Yes Go to 4 .

Yes Repair the open circuit in harness between ECM connector and engine ground.
CHECK FRONT OXYGEN (A/F) SENSOR.

Check the front oxygen (A/F) sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H6DO)>FRONT OXYGEN (A/F) SENSOR>INSPECTION .

Is the check result OK?

Repair the poor contact of ECM connector.

Replace the front oxygen (A/F) sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H6DO)>FRONT OXYGEN (A/F) SENSOR .