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Home >> Subaru >> 2013 >> Legacy Premium, Automatic CVT Trans >> Repair and Diagnosis >> External Pages >> Different car >> Section 26 (Engine Controls (Diagnostics) (H4DO)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0031 Ho2S Heater Control Circuit Low (Bank 1 Sensor 1) >> Wiring Diagram

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

WARNING: This page is about a different car, the 2013 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

Engine electrical system, non-turbo model < Refer to appropriate SYSTEM WIRING DIAGRAM. >

Fig 1: HO2S Heater Control Circuit Low - Wiring Diagram (Bank 1 Sensor 1)
G08570425Courtesy of SUBARU OF AMERICA, INC.
Step Check Yes No
1 CHECK POWER SUPPLY TO FRONT OXYGEN (A/F) SENSOR. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connectors from front oxygen (A/F) sensor.
  3. Turn the ignition switch to ON.
  4. Measure the voltage between front oxygen (A/F) sensor connector and engine ground.

    Connector & terminal 

    (E23) No. 2 (+) - Engine ground (-): 

 Is the voltage 10 V or more? Go to step 2  . Repair the power supply line.
NOTE: In this case, repair the following item:
  • Open circuit in harness between A/F, oxygen sensor relay connector and front oxygen (A/F) 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 FRONT OXYGEN (A/F) SENSOR CONNECTOR. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector from ECM.
  3. Measure the resistance between ECM and front oxygen (A/F) sensor connector.

    Connector & terminal 

    (B136) No. 5 - (E23) No. 1: 

    (B136) No. 6 - (E23) No. 1: 

 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 front oxygen (A/F) 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: 
(B134) No. 6 - Chassis ground: 
(B137) No. 1 - Chassis ground: 
(B137) 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 FRONT OXYGEN (A/F) SENSOR. 
Measure the resistance between front oxygen (A/F) sensor terminals.
Terminals 
No. 1 - No. 2: 		 Is the resistance 2 - 3 Ω? Repair the poor contact of ECM connector. Replace the front oxygen (A/F) sensor. < Refer to FRONT OXYGEN (A/F) SENSOR . >
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