Code explained

P0174: your engine is running lean on bank 2

P0174

In plain words: The engine is getting too much air or too little fuel on bank 2.
Standard name: System Too Lean (Bank 2)
System: Fuel and air mixture

General information, not a mechanic's diagnosis: have a mechanic confirm before any repair.

What the computer saw

The computer adds or takes away fuel to keep the mixture of air and fuel right, and it keeps a running total of how much it is adding, called fuel trim. When it has to add more fuel than its limit on bank 2, the side of a V6 or V8 that does not hold cylinder 1, it sets P0174. It means the engine is getting more air or less fuel than it measures on that side.

Likely causes, most common first

A vacuum leak. Air that gets in past the airflow sensor is not measured, so the mixture runs lean. Cracked hoses and intake gaskets are common places.
An airflow sensor that reads low. A dirty or failing mass airflow sensor under-reports the air coming in, so the computer adds too little fuel.
Low fuel pressure or a weak injector. A tired fuel pump, a clogged filter or a bank 2 injector that sprays too little all starve the mixture.
An exhaust leak before the bank 2 front oxygen sensor. Outside air drawn in at a leak makes the sensor read lean when the mixture is not.

What you can note yourself

Read every stored code. P0171 with it points at a cause both sides share; P0174 alone points at something on bank 2 only.
Note whether the idle is rough or high, or whether you hear a hiss from the engine bay.
Note any recent work on the intake, the airflow sensor or the fuel system.

What to tell the shop

All the codes, including any pending ones, and whether P0171 is among them.
Ask whether they read the fuel trims on both banks and tested for vacuum leaks before replacing parts.
Any recent work on the engine, intake or fuel system.

This page gives no verdict on whether a car is safe to drive; a mechanic can.

Questions people ask next

What does P0174 mean without P0171?

When only bank 2 is lean, the cause is usually on that side alone: an intake gasket, a hose, an injector or an exhaust leak near the bank 2 sensor. When both codes appear, look first at what both sides share, such as the airflow sensor or the fuel pressure.

What is bank 2?

Bank 2 is the row of cylinders that does not hold cylinder 1, on engines with two rows such as V6 and V8 engines.

Can a dirty airflow sensor cause P0174?

Yes. An airflow sensor that under-reads makes the whole engine run lean, which often sets P0171 as well.