DTC P2096 Post Catalyst Fuel Trim System Too Lean Bank 1: Notes

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

DTC detecting condition:

Detected when two consecutive driving cycles with fault occur.

CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Clear Memory Mode . and Inspection Mode Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Inspection Mode .
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 .

Fig 1: Engine Electrical System Wiring Diagram (Post Catalyst Fuel Trim System Lean Bank 1) - 1 Of 2

Courtesy of SUBARU OF AMERICA, INC.

Fig 2: Engine Electrical System Wiring Diagram (Post Catalyst Fuel Trim System Lean Bank 1) - 2 Of 2

Courtesy of SUBARU OF AMERICA, INC.

CHECK FOR ANY OTHER DTC ON DISPLAY .
Is any other DTC displayed?
- Yes: Check DTC using "List of Diagnostic Trouble Code (DTC)". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>List of Diagnostic Trouble Code (DTC) .
- No: Go to 2.
CHECK FRONT OXYGEN (A/F) SENSOR CONNECTOR AND COUPLING CONNECTOR .
Has water entered the connector?
- Yes: Completely remove any water inside.
- No: Go to 3.
CHECK HARNESS BETWEEN ECM AND FRONT OXYGEN (A/F) SENSOR CONNECTOR .
1. Turn the ignition switch to OFF.
2. Disconnect the connectors from front oxygen (A/F) sensor.
3. Disconnect the connector from ECM.
4. Measure the resistance of harness between ECM connector and front oxygen (A/F) sensor connector.
Connector & terminal

(B135) No. 57 - (E24) No. 3:

(B135) No. 33 - (E24) No. 4:

Is the resistance less than 1 Ω?
- Yes: Go to 4.
- No: 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
CHECK HARNESS BETWEEN ECM AND FRONT OXYGEN (A/F) SENSOR CONNECTOR .
Measure the resistance between ECM connector and chassis ground.

Connector & terminal

(B135) No. 57 - Chassis ground:

(B135) No. 33 - Chassis ground:

Is the resistance 1 MΩ or more?
- Yes: Go to 5.
- No: Repair the short circuit to ground in harness between ECM connector and front oxygen (A/F) sensor connector.
CHECK OUTPUT SIGNAL FOR ECM .
1. Connect the connector to ECM.
2. Turn the ignition switch to ON.
3. Measure the voltage between front oxygen (A/F) sensor connector and chassis ground.
Connector & terminal

(E24) No. 3 (+) - Chassis ground (-):

Is the voltage 4.5 V or more?
- Yes: Go to 7.
- No: Go to 6.
CHECK OUTPUT SIGNAL FOR ECM .
Measure the voltage between front oxygen (A/F) sensor connector and chassis ground.

Connector & terminal

(E24) No. 4 (+) - Chassis ground (-):

Is the voltage 4.95 V or more?
- Yes: Go to 7.
- No: Go to 8.
CHECK OUTPUT SIGNAL FOR ECM .
Measure the voltage between front oxygen (A/F) sensor connector and chassis ground.

Connector & terminal

(E24) No. 3 (+) - Chassis ground (-):

(E24) No. 4 (+) - Chassis ground (-):

Is the voltage 8 V or more?
- Yes: Repair the short circuit to power in the harness between ECM connector and front oxygen (A/F) sensor connector. After repair, replace the ECM. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Engine Control Module (ECM) .
- No: Repair the poor contact of ECM connector.
CHECK EXHAUST SYSTEM .
Are there holes or loose bolts on exhaust system?
- Yes: Repair the exhaust system.
- No: Go to 9.
CHECK AIR INTAKE SYSTEM .
Are there holes, loose bolts or disconnection of hose on air intake system?
- Yes: Repair the air intake system.
- No: Go to 10.
CHECK FUEL PRESSURE .
WARNING: Place "NO OPEN FLAMES" signs near the working area.

CAUTION: Be careful not to spill fuel.
1. Connect the front oxygen (A/F) sensor connector.
2. Measure the fuel pressure. Ref. to MECHANICAL(H4DO)>Fuel Pressure>INSPECTION .
CAUTION: Release fuel pressure before removing the fuel pressure gauge.

Is the measured value 340 - 400 kPa (3.5 - 4.1 kg/cm² , 49 - 58 psi)?
- Yes: Go to 11.
- No: Check the fuel pump and fuel delivery line. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Fuel Pump>INSPECTION . Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Fuel Delivery and Evaporation Lines>INSPECTION .
CHECK ENGINE COOLANT TEMPERATURE SENSOR .
1. Start the engine and warm up completely.
2. Using the Subaru Select Monitor or a general scan tool, read the value of [Coolant Temp.].
  NOTE:
  - Subaru Select Monitor
    For detailed procedures, refer to the Data Monitor. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Subaru Select Monitor .
  - General scan tool
    For detailed operation procedures, refer to the general scan tool operation manual.
Is the value of [Coolant Temp.] 75°C (167°F) or more?
- Yes: Go to 12.
- No: Replace the engine coolant temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Engine Coolant Temperature Sensor .
CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR .
1. Start the engine and warm up engine until coolant temperature is higher than 75°C (167°F).
2. For CVT models, set the select lever to "P" range or "N" range, and for MT models, place the shift lever in the neutral position.
3. Turn the A/C switch to OFF.
4. Turn all the accessory switches to OFF.
5. Read the value of Mass Air Flow using the Subaru Select Monitor or a general scan tool.
  NOTE:
  - Subaru Select Monitor
    For detailed procedures, refer to "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Subaru Select Monitor .
  - General scan tool
    For detailed operation procedures, refer to the general scan tool operation manual.
Is the value of intake air amount 2.0 - 5.0 g/s (0.26 - 0.66 lb/m)?
- Yes: Go to 13.
- No: Replace the mass air flow and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Mass Air Flow and Intake Air Temperature Sensor .
CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR .
1. Start the engine and warm up engine until coolant temperature is higher than 75°C (167°F).
2. For CVT models, set the select lever to "P" range or "N" range, and for MT models, place the shift lever in the neutral position.
3. Turn the A/C switch to OFF.
4. Turn all the accessory switches to OFF.
5. Open the front hood.
6. Measure the ambient temperature.
7. Using the Subaru Select Monitor or a general scan tool, read the value of [Intake Air Temp.].
  NOTE:
  - Subaru Select Monitor
    For detailed procedures, refer to the Data Monitor. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Subaru Select Monitor .
  - General scan tool
    For detailed operation procedures, refer to the general scan tool operation manual.
Subtract ambient temperature from [Intake Air Temp.]. Is the obtained value -10 - 50°C (-18 - 90°F)?
- Yes: Go to 14.
- No: Check the mass air flow and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Mass Air Flow and Intake Air Temperature Sensor .
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. Using the Subaru Select Monitor or a general scan tool, read the value of [Oxygen sensor #12].
  NOTE:
  - Depress the clutch pedal. (MT model)
  - Subaru Select Monitor
    For detailed procedures, refer to the Data Monitor. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Subaru Select Monitor .
  - General scan tool
    For detailed operation procedures, refer to the general scan tool operation manual.
Is the value of [Oxygen sensor #12] 0.490 V or more?
- Yes: Go to 15.
- No: Go to 16.
CHECK REAR OXYGEN SENSOR DATA .
1. Warm up the engine until engine coolant temperature is higher than 75°C (167°F), and rapidly reduce the engine speed from 3, 000 RPM.
2. Using the Subaru Select Monitor or a general scan tool, read the value of [Oxygen sensor #12].
  NOTE:
  - Depress the clutch pedal. (MT model)
  - Subaru Select Monitor
    For detailed procedures, refer to the Data Monitor. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Subaru Select Monitor .
  - General scan tool
    For detailed operation procedures, refer to the general scan tool operation manual.
Is the value of [Oxygen sensor #12] 0.250 V or less?
- Yes: Go to 17.
- No: Go to 16.
CHECK REAR OXYGEN SENSOR CONNECTOR AND COUPLING CONNECTOR .
Has water entered the connector?
- Yes: Completely remove any water inside.
- No: Go to 18.
CHECK FRONT OXYGEN (A/F) SENSOR USING REAR OXYGEN SENSOR SIGNAL .
1. Warm up the engine until engine coolant temperature is higher than 75°C (167°F), then keep the engine idling for 5 minutes or more.
2. Using the Subaru Select Monitor or a general scan tool, read the value of [Oxygen sensor #12].
  NOTE:
  - Subaru Select Monitor
    For detailed procedures, refer to the Data Monitor. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Subaru Select Monitor .
  - General scan tool
    For detailed operation procedures, refer to the general scan tool operation manual.
Is the value of [Oxygen sensor #12] kept at 0.250 V or less for 5 minutes or more?
- Yes: Replace the front oxygen (A/F) sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Front Oxygen (A/F) Sensor .
- No: Go to 18.
CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR .
1. Turn the ignition switch to OFF.
2. Disconnect the connector from rear oxygen sensor.
3. Disconnect the connector from ECM.
4. Measure the resistance of harness between ECM connector and rear oxygen sensor connector.
Connector & terminal

(B135) No. 57 - (E25) No. 3:

(B135) No. 56 - (E25) No. 4:

Is the resistance less than 1 Ω?
- Yes: Go to 19.
- No: 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
CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR .

Connect the connector to ECM.
Turn the ignition switch to ON.
Measure the voltage between rear oxygen sensor connector and chassis ground.

Connector & terminal

(E25) No. 3 (+) - Chassis ground (-):

Is the voltage 0.2 - 0.5 V?

Yes: Replace the rear oxygen sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Rear Oxygen Sensor .
No: 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