ENGINE (DIAGNOSTICS)(H4DOTC) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)

DTC P0140 O2 SENSOR CIRCUIT NO ACTIVITY DETECTED (BANK1 SENSOR 2)

DTC DETECTING CONDITION:

Detected when two consecutive driving cycles with fault occur.

CAUTION:

After repairing or replacing the defective part, perform the Clear Memory Mode and Inspection Mode .

WIRING DIAGRAM:

• LHD model

• RHD model

STEPCHECKYESNO

1.CHECK ANY OTHER DTC ON DISPLAY.

Is any other DTC displayed?

Check DTC using “List of Diagnostic Trouble Code (DTC)”.

NOTE:

In this case, it is not necessary to inspect DTC P0140.

2.CHECK REAR OXYGEN SENSOR DATA.

1) Warm-up the engine until engine coolant temperature is above 70°C (158°F), and keep the engine speed at 3,000 rpm. (Max. 2 min.)

2) Read the data of rear oxygen sensor signal using Subaru Select Monitor or general scan tool.

NOTE:

• For MT model, depress the clutch pedal.

• Subaru Select Monitor

For detailed operation procedure, refer to “READ CURRENT DATA FOR ENGINE”.

• General scan tool

For detailed operation procedure, refer to the general scan tool operation manual.

Is the voltage 490 mV or more?

3.CHECK REAR OXYGEN SENSOR DATA.

1) Warm-up the engine until engine coolant temperature is above 70°C (158°F), and rapidly reduce the engine speed from 3,000 rpm.

2) Read the data of rear oxygen sensor signal using Subaru Select Monitor or general scan tool.

NOTE:

• For MT model, depress the clutch pedal.

• Subaru Select Monitor

For detailed operation procedure, refer to “READ CURRENT DATA FOR ENGINE”.

• General scan tool

For detailed operation procedure, refer to the general scan tool operation manual.

Is the voltage 250 mV or less?

4.CHECK REAR OXYGEN SENSOR CONNECTOR AND COUPLING CONNECTOR.

Does water enter the connector?

Remove water thoroughly from the connector.

5.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 and rear oxygen sensor connector.

Connector & terminal

(B135) No. 4 — (T6) No. 3:
(B135) No. 30 — (T6) No. 4:

Is the resistance 3 Ω or more?

Repair the open circuit of harness between ECM and rear oxygen sensor connector.

6.CHECK HARNESS BETWEEN REAR OXYGEN SENSOR AND ECM CONNECTOR.

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 harness connector and chassis ground.

Connector & terminal

(T6) No. 3 (+) — Chassis ground (−):

Is the voltage 0.2 — 0.5 V?

Replace the rear oxygen sensor.

Repair the harness and connector.

NOTE:

In this case, repair the following item:

• Open circuit of harness between rear oxygen sensor and ECM connector

• Poor contact of the rear oxygen sensor connector

• Poor contact in ECM connector

7.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

• Looseness and improper fitting of parts 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.