P0174 fault code: fuel mixture too lean (Bank 2)
Plain-language definition
System Too Lean Bank 2
What does it mean?
This code mostly shows up on engines with their cylinders arranged in two banks; V engines and boxer engines are examples. Bank 2 is the side without cylinder 1, and its mixture is usually monitored separately by its own oxygen (lambda) sensor.
The engine computer corrects the mixture on each bank based on the oxygen sensor's readings. P0174 means this correction has reached its limit on Bank 2, that is, the engine computer has to add much more fuel than expected to balance the mixture. If P0171 is stored too, the cause may be a common source affecting both banks, such as the air flow sensor or the fuel pressure. If P0174 is on its own, a cause specific to that side, such as an air leak on that side, is more likely.
There may be no obvious symptoms. You may notice shaking at idle, hesitation when accelerating or a loss of power.
How serious is it?
It's rated Warning. If the lean mixture continues, combustion can become uneven and misfire codes may appear too.
Severity is a guide; if the warning light is flashing or you notice symptoms while driving, have the car checked at a workshop.
Common general causes
- Air leak on the intake side (vacuum hose, manifold gasket)
- Dirty or inaccurate air flow sensor (MAF)
- Low fuel pressure (fuel pump, fuel filter)
- Clogged injectors on this bank
- Exhaust leak before the Bank 2 oxygen sensor
- Oxygen (lambda) sensor giving wrong readings
The list shows general causes; a workshop finds the actual cause on your car with a check.
Definitions by make
Some manufacturers record the same code under their own wording:
- BMW
- System Too Lean
Related codes
How does it appear in the 2dakika report?
System Too Lean Bank 2
If the code is read as a confirmed (stored) fault, the report shows it with the "Warning" severity; in pending or past records, codes that don't request the warning light and aren't critical appear as "Info". If the engine computer stored them, the conditions when the fault was recorded (engine temperature, rpm, speed) are shown too.
Read this code with the OBD-X1, and clear it from the app after the repair.
Clearing the code doesn't fix the fault; if the problem persists, the code comes back.