Vacuum or intake air leak; Dirty or faulty mass air flow (MAF) sensor; Weak fuel pump or clogged fuel filter; Dirty or leaking fuel injector; Exhaust leak near the sensor.

Home / Check engine codes / P0171

P0171: System too lean (Bank 1)

Q: What does P0171 mean?

System too lean (Bank 1): The engine is getting too much air or too little fuel on bank 1. The computer cannot correct it with its normal adjustments.

Q: Can I drive with P0171?

Fix soon. Usually drivable for a short time, but get it checked soon. Ignoring it can waste fuel, raise emissions and lead to more damage.

Fix soonSystem: Fuel and air

What P0171 means

The engine is getting too much air or too little fuel on bank 1. The computer cannot correct it with its normal adjustments.

Common symptoms

Rough or unstable idle
Hesitation or poor acceleration
Worse fuel economy
Loss of power

Common causes

Vacuum or intake air leak
Dirty or faulty mass air flow (MAF) sensor
Weak fuel pump or clogged fuel filter
Dirty or leaking fuel injector
Exhaust leak near the sensor

Can I keep driving?

Fix soon. Usually drivable for a short time, but get it checked soon. Ignoring it can waste fuel, raise emissions and lead to more damage.

What to do next

Write down the code and any symptoms you notice.
Check the simple things first: the fuel cap, loose connectors and fluid levels where they apply.
Do not just clear the code. If the light comes back, the cause is still there and needs a proper diagnosis.
Read live data and freeze frame data with an OBD-II scanner app to see what the car was doing when the code was set.

Read P0171 from your own car

DriveHub connects to a $15 to $30 OBD-II adapter, reads the code from your car and explains it in plain English. iPhone and Android.

App Store Google Play Try the free code decoder

General information, not a diagnosis. Causes vary by make, model and engine. If you are unsure, have the car inspected.