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Home >> Subaru >> 2005 >> Outback R VDC Limited >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 8 (Engine Controls - Engine (Diagnostics) (H4SO)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0031 Ho2S Heater Control Circuit Low (Bank 1 Sensor 1)

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: 

CAUTION: After repair or replacement of faulty parts, conduct Clear Memory Mode < Ref. to , OPERATION , Clear Memory Mode.> and Inspection Mode < Ref. to , PROCEDURE , Inspection Mode.>.

WIRING DIAGRAM: 

Fig 1: DTC P0031 HO2S Heater Control Circuit Low (Bank 1 Sensor 1)
G03828443Courtesy of SUBARU OF AMERICA, INC.
DTC P0031 HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 SENSOR 1) DIAGNOSIS

Step Check Yes No
1. CHECK FOR ANY OTHER DTC ON DISPLAY.  Does the Subaru Select Monitor or OBD-II general scan tool display DTC P0031 and P0037 at the same time? Go to step 2.  Go to step 4. 
2. CHECK POWER SUPPLY TO FRONT OXYGEN (A/F) SENSOR. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector 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 

    (B395) No. 6 (+) - Engine ground (-): 

 Is the voltage 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 CURRENT DATA. 
  1. Start the engine.
  2. Read the data of front oxygen (A/F) sensor heater current using Subaru Select Monitor or OBD-II 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 general scan tool

    For detailed operation procedures, refer to the OBD-II general scan tool instruction manual .

 Is the current more 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 4. 
4. CHECK INPUT SIGNAL FROM ECM. 
  1. Start and idle the engine.
  2. Measure the voltage between ECM connector and chassis ground.

    Connector & terminal 

    (B134) No. 3(+) - Chassis ground (-): 

    (B134) No. 2 (+) - Chassis ground (-): 

 Is the voltage less than 1 V? Go to step 6.  Go to step 5. 
5. CHECK OUTPUT SIGNAL FROM ECM. 
Measure the voltage between ECM connector and chassis ground.
Connector & terminal 
(B134) No. 3 (+) - Chassis ground (-): 
(B134) No. 2 (+) - Chassis ground (-): 		 Does the voltage change by shaking the ECM harness and connector? Repair poor contact in ECM connector. Go to step 6. 
6. CHECK FRONT OXYGEN (A/F) SENSOR. 
  1. Turn the ignition switch to OFF.
  2. Measure the resistance between front oxygen (A/F) sensor connector terminals.

    Terminals 

    No. 4 - No. 6: 

 Is the resistance 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 the front oxygen (A/F) sensor. < Ref. to FRONT OXYGEN (A/F) SENSOR . >
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