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

WARNING: This page is about a different car, the 2006 Subaru Outback. However, it is still accessible from the selected car via links, so may be relevant.

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 repair or replacement of faulty parts, perform Clear Memory Mode < Ref. to OPERATION , Clear Memory Mode. > and Inspection Mode < Ref. to PROCEDURE , Inspection Mode. >.

WIRING DIAGRAM:

Fig 1: Front Oxygen (A/F) Sensor - Wiring Diagram

DTC P0031 HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 SENSOR 1) - DIAGNOSTIC PROCEDURE

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 (E47) 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 item: 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 GROUND CIRCUIT FOR ECM. Measure the resistance of harness between ECM connector and chassis ground. Connector & terminal (B134) No. 3 - Chassis ground: (B134) No. 5 - Chassis ground: (B137) No. 1 - Chassis ground: (B137) No. 2 - Chassis ground: (B137) No. 3 - Chassis ground: (B137) No. 7- Chassis ground:	Is the resistance less than 5 Ω?	Go to step 3.	Repair the harness and connector. NOTE: In this case, repair the following item: Open circuit in harness between ECM and engine ground terminal Poor contact in ECM connector Poor contact in coupling connector
3 CHECK CURRENT DATA. Start the engine. Read the data of the front oxygen (A/F) sensor heater current using the 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 procedures, refer to the "General Scan Tool Instruction 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 coupling connector Poor contact in ECM connector	Go to step 4.
4 CHECK OUTPUT SIGNAL OF ECM. Start and idle the engine. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B136) No. 2 (+) - Chassis ground (-): (B136) No. 3 (+) - 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. 2 (+) - Chassis ground (-): (B136) No. 3 (+) - Chassis ground (-):	Does the voltage change by shaking the ECM harness and connector while monitoring the value of voltage meter?	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. 2 - No. 1:	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 Poor contact in coupling connector	Replace the front oxygen (A/F) sensor. < Ref. to FRONT OXYGEN (A/F) SENSOR . >