P0174: System Too Lean (Bank 2)
The engine computer is adding extra fuel to bank 2 of a V6 or V8 because it sees too much air in the mix.
What P0174 means
P0174 is the bank 2 version of the lean code, so it only shows up on engines with two cylinder banks, such as V6 and V8 engines. Bank 2 is the side that does not contain cylinder 1. The front oxygen sensor on that side is reporting lean exhaust, and the computer has raised long term fuel trim until it hits its limit, roughly 15 to 35 percent according to RepairPal. The big clue is whether P0171 is set too. When both banks are lean, look for causes that affect the whole engine: a MAF sensor reading low, weak fuel pressure or a large central vacuum leak. When only bank 2 is lean, look for a leak or injector problem on that side, such as an intake gasket or vacuum line. Shops compare fuel trims between banks at idle and at 2,500 RPM, then smoke test the intake. Replacing oxygen sensors rarely fixes it, so ask for a real diagnosis before buying parts.
Common symptoms
- Check engine light on, often with P0171
- Rough idle when warm or at stoplights
- Hesitation or misfire on acceleration
- Reduced power
- Possible hissing sound under the hood
Most common causes
- Vacuum leak at the intake manifold gasket on bank 2
- Cracked PCV hose or vacuum line
- Dirty or failing MAF sensor
- Weak fuel pump or clogged fuel filter
- Clogged fuel injectors on bank 2
- Exhaust leak ahead of the bank 2 oxygen sensor
What to check yourself first
If you also have P0171, the problem is likely shared by both banks, like a MAF sensor, fuel pressure or a central vacuum leak. If only P0174 is set, focus on the bank 2 side of the intake. Check hoses and the PCV system for cracks and listen for hissing.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Smoke test for vacuum leaks | $61-$90 | Finds the leak, which is the usual cause when both P0171 and P0174 are present. |
| Replace intake manifold gasket | $683-$834 | Common on V6 and V8 engines when the gasket shrinks with age. |
| Clean the MAF sensor yourself | $15-$20 | A can of CRC MAF cleaner costs about $17. Clean before replacing. |
| Replace mass airflow (MAF) sensor | $274-$381 | If live airflow numbers are too low for the engine size. |
| Replace fuel pump | $1,344-$1,513 | Only if a fuel pressure test shows a weak pump. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0171 System Too Lean (Bank 1)
- P0175 System Too Rich (Bank 2)
- P0101 Mass or Volume Air Flow "A" Circuit Range/Performance
- P0300 Random/Multiple Cylinder Misfire Detected
- P0150 O2 Sensor Circuit (Bank 2 Sensor 1)