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:

Immediately at fault recognition
GENERAL DESCRIPTION < Ref. to DTC P0031 HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 SENSOR 1) , Diagnostic Trouble Code (DTC) Detecting Criteria. >

CAUTION: After repairing or replacing the defective part, perform the Clear Memory Mode < Ref. to OPERATION , Clear Memory Mode. > and Inspection Mode < Ref. to PROCEDURE , Inspection Mode. >.

WIRING DIAGRAM:

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

DIAGNOSIS PROCEDURE

Step	Check	Yes	No
1 CHECK ANY OTHER DTC ON DISPLAY.	Are other DTCs displayed on the Subaru Select Monitor and general scan tool?	Go to step 2.	Go to step 3.
2 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 (E22) No. 6 (+) - Engine ground (-):	Is the voltage more than 10 V?	Go to step 3.	Repair the power supply line. NOTE: In this case, repair the following item: Open circuit of harness between main relay and front oxygen (A/F) sensor connector Poor contact in front oxygen (A/F) sensor connector Poor contact of main relay connector
3 CHECK CURRENT DATA. Start the engine. Read the data of front oxygen (A/F) sensor heater current using Subaru Select Monitor or general scan tool. NOTE: Subaru Select Monitor For detailed operation procedure, refer to "READ CURRENT DATA FOR ENGINE". < Ref. to SUBARU SELECT MONITOR . > General scan tool For detailed operation procedure, refer to the general scan tool operation manual.	Is the current more than 0.2 A?	Repair the poor contact of connector. NOTE: In this case, repair the following item: Poor contact in front oxygen (A/F) sensor connector Poor contact in ECM connector	Go to step 4.
4 CHECK INPUT SIGNAL OF ECM. Start and idle the engine. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B136) No. 3 (+) - Chassis ground (-): (B136) No. 2 (+) - Chassis ground (-):	Is the voltage less than 1 V?	Go to step 6.	Go to step 5.
5 CHECK OUTPUT SIGNAL OF ECM. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B136) No. 3 (+) - Chassis ground (-): (B136) No. 2 (+) - Chassis ground (-):	Does the voltage change by shaking the ECM harness and connector?	Repair the poor contact of ECM connector.	Go to step 6.
6 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. 4 - No. 6:	Is the resistance less than 10 Ω?	Repair the harness and connector. NOTE: In this case, repair the following item: Open or ground short circuit of harness between front oxygen (A/F) sensor and ECM connector Poor contact in front oxygen (A/F) sensor connector Poor contact in ECM connector	Replace the front oxygen (A/F) sensor. < Ref. to FRONT OXYGEN (A/F) SENSOR . >