DTC P0037: A/F/O2 Heater Control Circuit Low Bank 1 Sensor 2: Notes

WARNING: This page is about a different variant/trim than selected.

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DTC detecting condition:

Detected when two consecutive driving cycles with fault occur.

Wiring diagram:

Engine Electrical System Ref. to WIRING SYSTEM (IMPREZA MODEL)>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM . Ref. to WIRING SYSTEM (CROSSTREK MODEL (EXCEPT FOR HEV))>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .
- IMPREZA MODEL
Courtesy of SUBARU OF AMERICA, INC.
- CROSSTREK MODEL
Courtesy of SUBARU OF AMERICA, INC.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.0 (EXCEPT FOR HEV))>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE CHECK BOARD .

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.0 (EXCEPT FOR HEV))>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

CHECK POWER SUPPLY TO REAR OXYGEN SENSOR .
1. Turn the ignition switch to OFF.
2. Disconnect the connector from the rear oxygen sensor.
3. Turn the ignition switch to ON.
4. Measure the voltage between rear oxygen sensor connector and engine ground.
  Connector and terminal
  
  (B19) No. 1 (+) - Engine ground (-):
  
  Is the voltage 10 V or more?
  
  Yes: Go to 2.
  
  No: Repair the power supply line. Or replace the main relay.
  NOTE:
  In this case, repair the following item:
  - Open circuit of harness between main relay connector and rear oxygen sensor connector
  - Poor contact of main relay connector
  - Defective main relay
CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR (OPEN) .
1. Turn the ignition switch to OFF.
2. Disconnect the connector from ECM.
3. Measure the resistance between ECM connector and oxygen sensor connector.
  Connector and terminal
  
  (B134) No. 22 - (B19) No. 2:
  
  Is the resistance less than 1 Ω?
  
  Yes: Go to 3.
  
  No: Repair the open circuit of harness between ECM connector and rear oxygen sensor connector.
CHECK GROUND CIRCUIT FOR ECM (OPEN CIRCUIT) .
Measure the resistance of harness between ECM connector and chassis ground.

Connector and terminal

(B134) No. 69 - Chassis ground:

(B134) No. 70 - Chassis ground:

(B134) No. 71 - Chassis ground:

(B134) No. 72 - Chassis ground:

Is the resistance less than 5 Ω?

Yes: Go to 4.

No: Check the harnesses and connectors, and repair or replace them if necessary.
NOTE:
In this case, repair the following item:
- Open circuit of harness between ECM connector and engine ground
- Poor contact of coupling connector
CHECK REAR OXYGEN SENSOR .
Check the rear oxygen sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO (EXCEPT FOR HEV))>REAR OXYGEN SENSOR>INSPECTION .

Is the check result OK?

Yes: Repair the poor contact of ECM connector.

No: Replace the rear oxygen sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO (EXCEPT FOR HEV))>REAR OXYGEN SENSOR .