P0170
T: DTC P0170 - FUEL TRIM MALFUNCTIONDTC DETECTING CONDITION:
- Two consecutive driving cycles with fault
TROUBLE SYMPTOM:
- Erroneous idling
- Engine stalls.
- Poor driving performance
CAUTION: After repair or replacement of faulty parts, conduct CLEAR MEMORY MODE and INSPECTION MODE. Refer to How To Clear Diagnostic Trouble Codes. Clearing Diagnostic Trouble Codes
10T1: CHECK EXHAUST SYSTEM.
CHECK: Are there holes or loose bolts on exhaust system?
YES: Repair exhaust system.
NO: Go to step 10T2.
10T2: CHECK AIR INTAKE SYSTEM.
CHECK: Are there holes, loose bolts or disconnection of hose on air intake system?
YES: Repair air intake system.
NO: Go to step 10T3.
10T3: CHECK FUEL PRESSURE.
1) Release fuel pressure.
(1) Remove fuel pump access hole lid located on the luggage compartment floor.
(2) Disconnect connector from fuel tank.
(3) Start engine and run it until it stalls.
(4) After stopping the engine,crank the engine for 4 or 5 seconds to reduce fuel pressure.
(5) Turn ignition switch OFF.
(6) Remove the fuel filler cap.
2) Connect connector to fuel tank.
3) Disconnect fuel delivery hose from fuel filter, and connect fuel pressure gauge.
4) Install fuel cap.
5) Start the engine and idle while gear position is neutral.
6) Measure fuel pressure while disconnecting pressure regulator vacuum hose from intake manifold.
WARNING: Before removing fuel pressure gauge, release fuel pressure.
NOTE:
If fuel pressure does not increase, squeeze fuel return hose 2 to 3 times, then measure fuel pressure again.
CHECK: Is fuel pressure between 284 and 314 kPa (2.9-3.2 kg/cm2, 41-46 psi)?
YES: Go to step 10T4.
NO: Repair the following items.
- Fuel pressure too high
- Clogged fuel return line or bent hose
- Fuel pressure too low
- Improper fuel pump discharge
- Clogged fuel supply line
10T4: CHECK FUEL PRESSURE.
After connecting pressure regulator vacuum hose, measure fuel pressure.
WARNING: Before removing fuel pressure gauge, release fuel pressure.
NOTE:
- If fuel pressure does not increase, squeeze fuel return hose 2 to 3 times, then measure fuel pressure again.
- If out of specification as measured at this step, check or replace pressure regulator and pressure regulator vacuum hose.
CHECK: Is fuel pressure between 206 and 235 kPa (2.1 -2.4 kg/cm2, 30-34 psi)?
YES: Go to step 10T5.
NO: Repair the following items.
- Fuel pressure too high
- Faulty pressure regulator
- Clogged fuel return line or bent hose
- Fuel pressure too low
- Faulty pressure regulator
- Improper fuel pump discharge
- Clogged fuel supply line
NOTE:
The fuel pressure gauge registers 10 to 20 kPa (0.1 to 0.2 kg/cm2, 1.4 to 2.8 psi) higher than standard valves during high-altitude operations.
10T5: CHECK ENGINE COOLANT TEMPERATURE SENSOR.
1) Turn ignition switch to OFF.
2) Connect the Subaru Select Monitor or the OBD-II general scan tool to data link connector.
3) Start the engine and warm-up completely.
4) Read data of engine coolant temperature sensor signal using Subaru Select Monitor or OBD-II general scan tool.
NOTE:
- Subaru Select Monitor
For detailed operation procedure, refer to the "READ CURRENT DATA SHOWN ON DISPLAY FOR ENGINE".
- OBD-II general scan tool
For detailed operation procedures, refer to the OBD-II General Scan Tool Instruction Manual.
CHECK: Is temperature greater than 60°C (140°F)?
YES: Go to step 10T6.
NO: Replace engine coolant temperature sensor.
10T6: CHECK MASS AIR FLOW SENSOR.
1) Start the engine and warm-up engine until coolant temperature is greater than 60°C (140°F).
2) Place the selector lever in "N" or "P" position.
3) Turn A/C switch to OFF.
4) Turn all accessory switches to OFF.
5) Read data of mass flow sensor signal using Subaru Select Monitor or OBD-II general scan tool.
NOTE:
- Subaru Select Monitor
For detailed operation procedure, refer to the "READ CURRENT DATA SHOWN ON DISPLAY FOR ENGINE".
- OBD-II general scan tool
For detailed operation procedures, refer to the OBD-II General Scan Tool Instruction Manual.
Specification:
CHECK: Is the voltage within the specifications?
YES: Contact with Subaru of America (SOA) service.
NOTE:
Inspection by Subaru of America's DTM is required, because probable cause is deterioration of multiple parts.
NO: Replace mass air flow sensor.