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:
- Two consecutive driving cycles with malfunction
CAUTION: After repair or replacement of malfunctioning parts, conduct Clear Memory Mode < Ref. to OPERATION , CLEAR MEMORY MODE > and INSPECTION MODE < Ref. to OPERATION , INSPECTION MODE. >
WIRING DIAGRAM:

Fig 1: HO2S Heater Control Circuit Wiring Diagram
Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE

Step	Check	Yes	No
1 CHECK ANY OTHER DTC ON DISPLAY.	Does the Subaru Select Monitor or general scan tool indicate DTC P1132 and P0141 at the same time?	Go to step 2.	Go to step 5.
2 CHECK POWER SUPPLY TO FRONT OXYGEN (A/F) SENSOR. Turn ignition switch to OFF. Disconnect connector from front oxygen (A/ F) sensor. Turn ignition switch to ON. Measure voltage between front oxygen (A/ F) sensor connector and engine ground. Connector & terminal (B18) No. 4 (+) - Engine ground (-):	Is the measured value more than 10 V?	Go to step 3.	Repair 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
3 CHECK GROUND CIRCUIT OF ECM. Measure resistance of harness between ECM connector and chassis ground. Connector & terminal (B136) No. 5 - Chassis ground: (B136) No. 16 - Chassis ground:	Is the measured value less than 5 Ω?	Go to step 4.	Repair harness and connector. NOTE: In this case, repair the following: Open circuit in harness between ECM and engine ground terminal Poor contact in ECM connector Poor contact in coupling connector
4 CHECK CURRENT DATA. Start engine Read 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 the "READ CURRENT DATA FOR ENGINE". < Ref. to SUBARU SELECT MONITOR . > OBD-II scan tool For detailed operation procedures, refer to the General Scan Tool Instruction Manual.	Is the measured value less than 0.2 A?	Repair poor contact in connector. NOTE: In this case, repair the following: Poor contact in front oxygen (A/F) sensor connector Poor contact in ECM connector	Go to step 6.
5 CHECK OUTPUT SIGNAL FROM ECM. Start and idle the engine. Measure voltage between ECM connector and chassis ground. Connector & terminal (B136) No. 6 (+) - Chassis ground (-): (B136) No. 17(+)- Chassis ground (-):	Is the measured value less than 1.0 V?	Go to step 7.	Go to step 6.
6 CHECK OUTPUT SIGNAL FROM ECM. Measure voltage between ECM connector and chassis ground. Connector & terminal (B136) No. 6 (+) - Chassis ground (-): (B136) No. 17(+) - Chassis ground (-):	Is the measured value less than 1.0 V shaking harness and connector of ECM while monitoring the value with voltage meter?	Repair poor contact in ECM connector.	Go to step 7.
7 CHECK FRONT OXYGEN (A/F) SENSOR. Turn ignition switch to OFF. Measure resistance between front oxygen (A/F) sensor connector terminals. Terminals No. 3 - No. 4:	Is the measured value less than 10 Ω?	Repair harness and connector. NOTE: In this case, repair the following: Open or ground short circuit in 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 front oxygen (A/F) sensor. < Ref. to FRONT OXYGEN (A/F) SENSOR . >