DTC P0037: A/F/O2 Heater Control Circuit Low 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 ENGINE (DIAGNOSTICS) (H4DO)>CLEAR MEMORY MODE>OPERATION ., and inspection mode Ref. to ENGINE (DIAGNOSTICS) (H4DO)>INSPECTION MODE>PROCEDURE .
Use the check board when measuring the ECM terminal voltage and resistance.

Wiring diagram:

Engine Electrical System Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

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?

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 M/B main relay connector and rear oxygen sensor connector
- Poor contact of M/B main relay connector
- Poor contact of coupling connector
- Defective M/B main relay
CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR 4k CONNECTOR .
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 & terminal
  
  (E158) No. 10 - (E25) 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 .
Measure the resistance of harness between ECM connector and chassis ground.

Connector & terminal

(E158) No. 61 - Chassis ground:

(E158) No. 62 - Chassis ground:

(E158) No. 63 - Chassis ground:

(E158) No. 64 - Chassis ground:

(E158) No. 65 - Chassis ground:

Is the resistance less than 5 Ω?

Yes: Go to 4 .

No: Repair the open circuit in harness between ECM connector and engine ground.
CHECK REAR OXYGEN SENSOR .
Check the rear oxygen sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>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)>REAR OXYGEN SENSOR .