Trouble code
P0171
System Too Lean (Bank 1)
What P0171 means
The engine is running with too much air for the fuel being delivered on bank 1. The computer has added fuel to compensate and has run out of adjustment range.
Symptoms you may notice
- Rough idle
- Hesitation on acceleration
- Poor fuel economy
- Occasional stalling
Common causes, cheapest first
- Vacuum leak in an intake hose or gasket
- Dirty or failing mass airflow sensor
- Weak fuel pump or clogged filter
- Leaking intake manifold gasket
- Failing PCV valve or hose
- Exhaust leak ahead of the oxygen sensor
Before you buy anythingDo not buy an oxygen sensor for this code. The sensor is usually reporting a real lean condition accurately. Find the unmetered air first, and check the cheapest cause, a cracked intake hose, before anything else.
What to do next
- Confirm the code with your own scan tool, or have it read free at a chain parts store.
- Decode your VIN so you know your exact engine and build date.
- Work down the causes above from cheapest to most expensive.
- Search NHTSA for a recall or service bulletin covering this symptom on your vehicle.
- Read the engine buying guide before ordering.
P0171 is a generic OBD-II code, standardized across every make and model sold in the US from 1996 onward. The meaning is the same on any vehicle; the specific part and its location are not.
Parts
Parts commonly needed for P0171
These go to Amazon. We earn a commission if you buy, at no extra cost to you — see our affiliate disclosure. Which one you actually need depends on diagnosis — read the note above first.
Confirm fitment against your VIN on the listing page before ordering. A part that matches your year and model can still be wrong for your build date or engine code.