Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc p0137 o2 sensor circuit low voltage bank 1 sensor 2

Subaru Legacy BN/BS (2015-2019) Service Manual / Engine (diagnostics)(h6do) / Diagnostic procedure with diagnostic trouble code (dtc) / Dtc p0137 o2 sensor circuit low voltage bank 1 sensor 2

DTC DETECTING CONDITION:

Detected when two consecutive driving cycles with fault occur.

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 REAR OXYGEN SENSOR DATA. 1) Warm up the engine until engine coolant temperature is higher than 75°C (167°F), and keep the engine speed at 3,000 rpm. (2 minutes maximum) 2) Keep the engine speed at idle. (One minute) 3) Read the value of «Front O2 Sensor #1» using the Subaru Select Monitor or a general scan tool. NOTE: • Subaru Select Monitor For detailed operation procedures, refer to “Read Current Data For Engine”. Subaru Select Monitor • General scan tool For detailed operation procedures, refer to the general scan tool operation manual.	Is the value of «Front O2 Sensor #1» 0.490 V or more-	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0137 O2 SENSOR CIRCUIT LOW VOLTAGE BANK 1 SENSOR 2	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0137 O2 SENSOR CIRCUIT LOW VOLTAGE BANK 1 SENSOR 2
2.CHECK REAR OXYGEN SENSOR CONNECTOR AND COUPLING CONNECTOR.	Has water entered the connector-	Completely remove any water inside.	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0137 O2 SENSOR CIRCUIT LOW VOLTAGE BANK 1 SENSOR 2
3.CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR. 1) Turn the ignition switch to OFF. 2) Disconnect the connector from ECM and rear oxygen sensor. 3) Measure the resistance of harness between ECM connector and rear oxygen sensor connector. Connector & terminal (E158) No. 57 — (E61) No. 3: (E158) No. 56 — (E61) No. 4:	Is the resistance less than 1 --	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0137 O2 SENSOR CIRCUIT LOW VOLTAGE BANK 1 SENSOR 2	Repair the harness and connector. NOTE: In this case, repair the following item: • Open circuit in harness between ECM connector and rear oxygen sensor connector • Poor contact of coupling connector
4.CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR. 1) Connect the connector to ECM. 2) Turn the ignition switch to ON. 3) Measure the voltage between rear oxygen sensor connector and chassis ground. Connector & terminal (E61) No. 3 (+) — Chassis ground (−):	Is the voltage 1.18 V or more-	Replace the rear oxygen sensor. Rear Oxygen Sensor	Repair the harness and connector. NOTE: In this case, repair the following item: • Open circuit in harness between ECM connector and rear oxygen sensor connector • Poor contact of ECM connector • Poor contact of coupling connector
5.CHECK EXHAUST SYSTEM. Check exhaust system parts. NOTE: Check the following items. • Looseness and improper fitting of exhaust system parts • Damage (crack, hole etc.) of parts • Loose part and improper installation between front oxygen (A/F) sensor and rear oxygen sensor	Is there any fault in exhaust system-	Repair or replace faulty parts.	Replace the rear oxygen sensor. Rear Oxygen Sensor

1. OUTLINE OF DIAGNOSIS

Detect for NG of the rear oxygen sensor continuity.

Judge as NG if the rear oxygen sensor voltage value is not within the range.

2. COMPONENT DESCRIPTION

(A)	Electromotive force	(B)	Air fuel ratio	(C)	Lean
(D)	Rich	(E)	Theoretical air fuel ratio	(F)	Comparative voltage

(1)	Atmosphere	(2)	Exhaust gas	(3)	Electromotive force

3. EXECUTION CONDITION

Secondary Parameters	Execution condition
Judgment 1
Battery voltage	≥ 10.9 V
Judgment 2,3
Battery voltage	≥ 10.9 V
Estimated secondary oxygen sensor element temperature	≥ 500 °C (932 °F)
Rear oxygen sensor offset voltage	≥ 1.28 V and > 1.68 V
Accumulated duty ratio of the rear oxygen sensor heater operation since engine started	≥ Value from Map

Map

Engine coolant temperature at engine starting

°C (°F)

−40

(−40)

−30

(−22)

−20

(−4)

−10

(14)

(32)

(50)

(68)

(86)

Accumulated duty ratio of the rear oxygen sensor heater operation since engine started

10500

Engine coolant temperature at engine starting

°C (°F)

(104)

(122)

(140)

(158)

(176)

(194)

100

(212)

110

(230)

Accumulated duty ratio of the rear oxygen sensor heater operation since engine started

10500

4. GENERAL DRIVING CYCLE

Perform the diagnosis continuously after the enable conditions have been established.

5. DIAGNOSTIC METHOD

If the duration of time while the following conditions are met is longer than the time indicated, judge as NG.

Judgment Value

Malfunction Criteria	Threshold Value
Judgment 1: Short to ground
Secondary oxygen sensor offset signal	< 1.28 V
Judgment 2: Circuit open
Secondary oxygen sensor signal	< 1.18 V
Judgment 3: Out of range
Secondary oxygen sensor output voltage	< −0.22 V

Time Needed for Diagnosis: 1000 ms

Malfunction Indicator Light Illumination: Illuminates when malfunction occurs in 2 continuous driving cycles.

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