ENGINE (DIAGNOSTICS)(H4DO) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)

DTC P0172 SYSTEM TOO RICH (BANK 1)

DTC DETECTING CONDITION:

Two consecutive driving cycles with fault

TROUBLE SYMPTOM:

• Improper idling

• Engine stalls.

• Poor driving performance

CAUTION:

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

STEPCHECKYESNO

1.CHECK EXHAUST SYSTEM.

Are there holes or loose bolts on exhaust system?

Repair the exhaust system.

2.CHECK AIR INTAKE SYSTEM.

Are there holes, loose bolts or disconnection of hose on air intake system?

Repair the air intake system.

3.CHECK FUEL PRESSURE.

WARNING:

• Place “NO OPEN FLAMES” signs near the working area.

• Be careful not to spill fuel.

Measure the fuel pressure.

WARNING:

Release fuel pressure before removing the fuel pressure gauge.

Is the measured value 340 — 361 kPa (3.5 — 3.7 kgf/cm2, 49 — 52 psi)?

Repair the following item.

Fuel pressure is too high:

• Clogged fuel line or bent hose

Fuel pressure is too low:

• Improper fuel pump discharge

• Clogged fuel line

4.CHECK ENGINE COOLANT TEMPERATURE SENSOR.

1) Start the engine and warm-up completely.

2) Read the data of engine coolant temperature sensor signal using Subaru Select Monitor or general scan tool.

NOTE:

• Subaru Select Monitor

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

• General scan tool

For detailed operation procedures, refer to the “General Scan Tool Instruction Manual”.

Is the temperature above 60°C (140°F)?

Replace the engine coolant temperature sensor.

5.CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR.

1) Start the engine and warm-up engine until coolant temperature is greater than 60°C (140°F).

2) Place the shift lever in neutral position.

3) Turn the A/C switch to OFF.

4) Turn all the accessory switches to OFF.

5) Read the data of mass air flow and intake air temperature sensor signal using Subaru Select Monitor or general scan tool.

NOTE:

• Subaru Select Monitor

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

• General scan tool

For detailed operation procedures, refer to the “General Scan Tool Instruction Manual”.

Is the measured value in the following range? Is the measured value 2.1 — 3.4 g/s (0.28 — 0.45 lb/m)?

Replace the mass air flow and intake air temperature sensor.

6.CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR.

1) Start the engine and warm-up engine until coolant temperature is greater than 60°C (140°F).

2) Place the shift lever in 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) Read the data of mass air flow and intake air temperature sensor signal using Subaru Select Monitor or general scan tool.

NOTE:

• Subaru Select Monitor

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

• General scan tool

For detailed operation procedures, refer to the “General Scan Tool Instruction Manual”.

Subtract the ambient temperature from intake air temperature. Is the obtained value −10 — 50°C (−18 — 90°F)?

Contact with SUBARU distributor service.

NOTE:

The probable cause is considered as the deterioration of multiple parts.

Check the mass air flow and intake air temperature sensor.