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

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

DTC DETECTING CONDITION:

Detect as soon as the malfunction occurs.
GENERAL DESCRIPTION < Ref. to DTC P0031 HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 SENSOR 1) , Diagnostic Trouble Code (DTC) Detecting Criteria. >

CAUTION: After repair or replacement of faulty parts, conduct Clear Memory Mode < Ref. to , OPERATION , Clear Memory Mode.> and Inspection Mode < Ref. to , PROCEDURE , Inspection Mode.>.

WIRING DIAGRAM:

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

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE (DTC P0031)

Step	Check	Yes	No
1 CHECK POWER SUPPLY TO FRONT OXYGEN (A/F) SENSOR. Turn the ignition switch to OFF. Disconnect the connector 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 (B18) No. 2 (+) - Engine ground (-):	Is the voltage more than 10 V?	Go to step 2.	Repair the power supply line. NOTE: In this case, repair the following: Open circuit in harness between main relay and front oxygen (A/F) sensor connector Poor contact in front oxygen (A/F) sensor connector Poor contact in main relay connector
2 CHECK HARNESS BETWEEN FRONT OXYGEN (A/F) SENSOR AND ECM. Turn the ignition switch to OFF. Disconnect the connectors from ECM. Measure the voltage between front oxygen (A/F) sensor connector and ECM. Connector & terminal (B18) No. 1 - (B134) No. 2: B18 No. 1 - (B134) No. 3:	Is the resistance less than 1 ?	Go to step 3.	Repair the open circuit in harness between ECM and front oxygen (A/F) sensor.
3 CHECK HARNESS BETWEEN FRONT OXYGEN (A/F) SENSOR AND ECM. Measure the resistance between ECM connector and chassis ground. Connector & terminal (B134) No. 2 - Chassis ground: (B134) No. 3 - Chassis ground:	Is the resistance more than 1 M?	Go to step 4.	Repair the ground short circuit in harness between ECM and front oxygen (A/F) sensor.
4 CHECK FRONT OXYGEN (A/F) SENSOR. Turn the ignition switch to OFF. Measure the resistance between front oxygen (A/F) sensor connector terminals. Terminals No. 1 - No. 2:	Is the resistance 2.4 ?	Repair the poor contact in ECM connector.	Replace the front oxygen (A/F) sensor. < Ref. to FRONT OXYGEN (A/F) SENSOR . >