Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc p0051 a/f / o2 heater control circuit low bank 2 sensor 1

Subaru Legacy BN/BS (2015-2019) Service Manual / Engine (diagnostics)(h6do) / Diagnostic procedure with diagnostic trouble code (dtc) / Dtc p0051 a/f / o2 heater control circuit low bank 2 sensor 1

DTC DETECTING CONDITION:

Immediately at fault recognition

CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Mode Clear Memory Mode > OPERATION, and Inspection Mode Inspection Mode > PROCEDURE.

WIRING DIAGRAM:

• Engine Electrical System ENGINE TYPE EZ (WITHOUT PUSH BUTTON START) Engine Electrical System > WIRING DIAGRAM

• Engine Electrical System ENGINE TYPE EZ (WITH PUSH BUTTON START) Engine Electrical System > WIRING DIAGRAM

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 (E24) No. 2 (+) — Engine ground (−):	Is the voltage 10 V or more-	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0051 A/F / O2 HEATER CONTROL CIRCUIT LOW BANK 2 SENSOR 1	Repair the power supply line. NOTE: In this case, repair the following item: • Open circuit of harness between M/B main relay and front oxygen (A/F) sensor connector • Poor contact of M/B main relay connector • Poor contact of coupling connector • Defective M/B main relay • Blown out of fuse (M/B No. 20)
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 connector and front oxygen (A/F) sensor connector. Connector & terminal (E158) No. 4 — (E24) No. 1:	Is the resistance less than 1 --	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0051 A/F / O2 HEATER CONTROL CIRCUIT LOW BANK 2 SENSOR 1	Repair the harness and connector. NOTE: In this case, repair the following item: • Open circuit in harness between ECM connector 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 connector and chassis ground. Connector & terminal (E158) No. 60 — Chassis ground: (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 --	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0051 A/F / O2 HEATER CONTROL CIRCUIT LOW BANK 2 SENSOR 1	Repair the open circuit in harness between ECM connector and engine ground.
4.CHECK FRONT OXYGEN (A/F) SENSOR. Measure the resistance between front oxygen (A/F) sensor connector terminals. Terminals No. 2 — No. 1:	Is the resistance 2 — 3 --	Repair the poor contact of ECM connector.	Replace the front oxygen (A/F) sensor. Front Oxygen (A/F) Sensor

1. OUTLINE OF DIAGNOSIS

NOTE:

For the detection standard, refer to DTC P0031. Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0031 A/F / O2 HEATER CONTROL CIRCUIT LOW BANK 1 SENSOR 1

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