ENGINE (DIAGNOSTICS)(H4SO) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)

DTC P0172 SYSTEM TOO RICH (BANK 1)

DTC DETECTING CONDITION:

Detected when two consecutive driving cycles with fault occur.

TROUBLE SYMPTOM:

Erroneous 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.

1) Release the fuel pressure.

(1) Disconnect the connector from fuel pump relay.

(2) Start and idle the engine until the engine stalls.

(3) After the engine stalls, crank it for five more seconds.

(4) Turn the ignition switch to OFF.

2) Connect the connector to the fuel pump relay.

3) Disconnect the fuel delivery hose, and connect the fuel pressure gauge.

4) Install the fuel filler cap.

5) Start the engine and idle while gear position is neutral.

6) Measure the fuel pressure while disconnecting pressure regulator vacuum hose from intake manifold.

WARNING:

Release fuel pressure before removing the fuel pressure gauge.

NOTE:

If fuel pressure does not increase, squeeze fuel return hose 2 to 3 times, then measure fuel pressure again.

Is the measured value 284 — 314 kPa (2.9 — 3.2 kgf/cm2, 41 — 46 psi)?

Repair the following item.

Fuel pressure is too high:

Clogged fuel return line or bent hose

Fuel pressure is too low:

Improper fuel pump discharge

Clogged fuel supply line

4.CHECK FUEL PRESSURE.

After connecting the pressure regulator vacuum hose, measure fuel pressure.

WARNING:

Release fuel pressure before removing the fuel pressure gauge.

NOTE:

If fuel pressure does not increase, squeeze fuel return hose 2 to 3 times, then measure fuel pressure again.

If the measured value at this step is out of specification, check or replace pressure regulator and pressure regulator vacuum hose.

Is the measured value 206 — 235 kPa (2.1 — 2.4 kgf/cm2, 30 — 34 psi)?

Repair the following item.

Fuel pressure is too high:

Faulty pressure regulator

Clogged fuel return line or bent hose

Fuel pressure is too low:

Faulty pressure regulator

Improper fuel pump discharge

Clogged fuel supply line

5.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.

NOTE:

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

Is the engine coolant temperature 60°C (140°F) or higher?

Replace the engine coolant temperature sensor.

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

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

2) Place the select lever in “N” or “P” 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:

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

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.

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

1) Start the engine and warm-up engine until coolant temperature is higher 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:

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

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

Contact the SUBARU distributor service.

Check the mass air flow and intake air temperature sensor.