DTC P0037 Ho2S Heater Control Circuit Low (Bank 1 Sensor 2): Wiring Diagram

Engine electrical system, 2.5 L model (without push button start). See appropriate SYSTEM WIRING DIAGRAM article.
Engine electrical system, 2.5 L model (with push button start). See appropriate SYSTEM WIRING DIAGRAM article.

Fig 1: Heater Control - Circuit Diagram (Low, Bank 1 Sensor 2)
Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE

Step	Check	Yes	No
1 CHECK POWER SUPPLY TO REAR OXYGEN SENSOR. Turn the ignition switch to OFF. Disconnect the connector from rear oxygen sensor. Turn the ignition switch to ON. Measure the voltage between rear oxygen sensor connector and engine ground. Connector & terminal (E25) No. 1 (+) - Engine ground (-):	Is the voltage 10 V or more?	Go to step 2 .	Repair the power supply line. Or replace the main relay. NOTE: In this case, repair the following item: Open circuit in harness between A/F, oxygen sensor relay connector and rear oxygen sensor connector Poor contact of A/F, oxygen sensor relay connector Poor contact of coupling connector Malfunction of A/F, oxygen sensor relay
2 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR. Turn the ignition switch to OFF. Disconnect the connector from ECM. Measure the resistance between ECM and oxygen sensor connector. Connector & terminal (B134) No. 6 - (E25) No. 2:	Is the resistance less than 1 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 rear oxygen sensor connector Poor contact of coupling connector
3 CHECK GROUND CIRCUIT FOR ECM. Measure the resistance of harness between ECM and chassis ground. Connector & terminal (B134) No. 3 - Chassis ground: (B134) No. 4 - Chassis ground: (B136) No. 1 - Chassis ground: (B136) No. 2 - Chassis ground: (B136) 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 and engine ground Poor contact of coupling connector
4 CHECK REAR OXYGEN SENSOR. Measure the resistance between rear oxygen sensor terminals. Terminals No. 2 - No. 1:	Is the resistance 5 - 7 Ω?	Repair the poor contact of ECM connector.	Replace the rear oxygen sensor. Refer to REAR OXYGEN SENSOR .