P0171: Mixture too lean (bank 1)
Bank 1 is getting too much air or too little fuel. The most common causes are an air leak in the intake or a dirty air flow meter.
| Code | P0171 |
|---|---|
| System | Engine and transmission |
| Group | P01xx, Air and fuel metering |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0171 means
A lean mixture means there is more air than the injected fuel calls for. The ECU tries to compensate by adding fuel, and this code is set when it reaches the limit of what it can correct. On inline engines, bank 1 is the whole engine.
Most common causes
- Cracked or loose vacuum hose, or split intake hose after the air flow meter
- Dirty air flow meter reading less air than is really entering
- Leaking intake manifold gasket or crankcase ventilation (PCV) valve
- Blocked fuel filter or weak fuel pump
- Dirty or partly clogged injectors
- Exhaust leak ahead of the oxygen sensor
Symptoms
- Engine warning light on
- Unsteady or hunting idle
- Hesitation or lack of power when accelerating
- Hissing sound in the engine bay (if there is an air leak)
- Hard starting
Can you drive with P0171?
With care You can drive, but a lean mixture over time can cause misfires and make the engine and catalytic converter run hotter. Have it checked soon.
Open the bonnetthe in-depth explanation
How to check it
Watch the long term fuel trim for bank 1 in live data: if it is very high at idle and falls as revs rise, an air leak is most likely; if it also rises under load, it points to a lack of fuel. With the engine running, listen for a hiss.
How to read and clear P0171 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0171 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P016D Fuel pressure control takes too long to enter closed loop operation
- P016E The closed loop fuel pressure control in the limit pressure gives a higher
- P016F The closed loop fuel pressure control in the limit pressure gives a lower
- P0170 Fuel trim out of limits (bank 1)
- P0172 System running too rich (bank 1)
- P0173 Fuel trim malfunction (bank 2)
- P0174 System running too lean (bank 2)
- P0175 System running too rich (bank 2)
- P0100 Mass or volume air flow sensor circuit fault
- P0101 Air flow sensor range or performance problem
- P0102 Air flow sensor circuit low input
- P0103 Air flow sensor circuit high input
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: Knock and pre-ignition.
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: Misfires, catalyst and lambda sensors.
What does code P0171 mean?
A lean mixture means there is more air than the injected fuel calls for. The ECU tries to compensate by adding fuel, and this code is set when it reaches the limit of what it can correct. On inline engines, bank 1 is the whole engine.
Can you drive with P0171?
You can drive, but a lean mixture over time can cause misfires and make the engine and catalytic converter run hotter. Have it checked soon.
How do you clear P0171?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0171 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
