2017 Subaru WRX BaseFACTORY OEM SERVICE PROCEDURE

DTC P0141 O2 Sensor Heater Circuit Bank 1 Sensor 2: Notes

DTC DETECTING CONDITION: 

Detected when two consecutive driving cycles with fault occur.

CAUTION:
  • After servicing or replacing faulty parts, perform Clear Memory Mode <Ref. to OPERATION , Clear Memory Mode.>, and Inspection Mode <Ref. to PROCEDURE , Inspection Mode.>.
  • Use the check board when measuring the ECM terminal voltage and resistance.

WIRING DIAGRAM: 

Engine Electrical System <Ref. to WIRING DIAGRAM , Engine Electrical System.>

Fig 1: A/F/O2 Heater Control Circuit Low Bank 1 Sensor 2 - Wiring Diagram
G11577050Courtesy of SUBARU OF AMERICA, INC.
Step Check Yes No
1 CHECK POWER SUPPLY TO REAR OXYGEN SENSOR. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector from rear oxygen sensor.
  3. Turn the ignition switch to ON.
  4. 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.
NOTE: In this case, repair the following item:
  • Open circuit in harness between A/F, oxygen sensor relay 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. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector from ECM.
  3. Measure the resistance between ECM connector and rear oxygen sensor connector.

    Connector & terminal 

    (E25) No. 2 - (E159) No. 3: 

 Is the resistance less than 1 Ω? Go to step 3  . Repair the open circuit of harness between ECM connector and rear oxygen sensor connector.
3 CHECK GROUND CIRCUIT FOR ECM. 
Measure the resistance of harness between ECM connector and engine ground.
Connector & terminal 
(B134) No. 35 - Engine ground: 
(B134) No. 47 - Engine ground: 
(E159) No. 10 - Engine ground: 
(E159) No. 17 - Engine ground: 
(E159) No. 18 - Engine ground: 
(E159) No. 25 - Engine ground: 
(E159) No. 26 - Engine 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 connector and engine ground
  • Poor contact of coupling connector
4 CHECK REAR OXYGEN SENSOR. 
Measure the resistance between rear oxygen sensor connector terminals.
Terminals 
No. 1 - No. 2: 		 Is the resistance 5.4 - 7.3 Ω? Repair the poor contact of ECM connector. Replace the rear oxygen sensor. <Ref. to Rear Oxygen Sensor .>
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.