DTC P0031 Ho2S Heater Control Circuit Low (Bank 1 Sensor 1): Wiring Diagram

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

Engine Electrical System ENGINE TYPE EJ (WITHOUT PUSH BUTTON START) <Ref. to 2.5L TURBO (WITHOUT PUSH BUTTON START), WIRING DIAGRAM, Engine Electrical System.>
Engine Electrical System ENGINE TYPE EJ (WITH PUSH BUTTON START) <Ref. to 2.5L TURBO (WITH PUSH BUTTON START), WIRING DIAGRAM, Engine Electrical System.>

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

G10265804

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE

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 (B379) No. 1 (+) - 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 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 (B136) No. 5 - (B379) No. 2: (B136) No. 6 - (B379) No. 2:	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 chassis ground. Connector & terminal (B134) No. 3 - Chassis ground: (B134) No. 4 - Chassis ground: (B134) No. 6 - Chassis ground: (B137) No. 1 - Chassis ground: (B137) No. 3 - Chassis 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. 1 - No. 2:	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 .>