P0174 means “System Too Lean (Bank 2).” It is the Bank 2 twin of the P0171 guide code. Bank 2 is the side of a V6 or V8 engine that does not contain cylinder number one. The engine computer sees too much oxygen in the exhaust on that bank, adds fuel to compensate, and when it runs out of correction room it stores P0174.
What P0174 tells you
Every engine tries to hold a balanced air to fuel ratio. When the mixture on Bank 2 goes lean, the oxygen sensor reports it and the computer raises the fuel trim to add fuel. If the fuel it adds is not enough to bring the mixture back to normal, the correction maxes out and P0174 is set. On inline engines there is only one bank, so you will see P0171 instead.
P0171 and P0174 together
When both P0171 and P0174 are stored at the same time, the cause almost always affects the whole engine, not one side. Think of a shared vacuum leak, a dirty MAF sensor, low fuel pressure, or a failing PCV system. A leak or fault on just one bank tends to set only P0171 or only P0174, which is a useful clue during diagnosis.
Symptoms of P0174
Driving symptoms
- A check engine light, sometimes flashing under load
- Rough or unstable idle
- Hesitation or a stumble on acceleration
- Slightly reduced fuel economy
- Occasional stalling at idle or when coming to a stop
Technical symptoms
- High positive short-term and long-term fuel trim on Bank 2
- Lean readings that are worse at idle if a vacuum leak is present
- Airflow readings that do not match engine load if the MAF is dirty
Common causes of P0174
- A vacuum or intake leak on the Bank 2 side or shared with both banks. See vacuum leak.
- A dirty or failing MAF sensor that under-reports airflow.
- Weak fuel delivery from a tired fuel pump or a clogged filter.
- A failing upstream oxygen sensor on Bank 2.
- A leaking PCV valve or hose.
- An exhaust leak ahead of the Bank 2 oxygen sensor that lets outside air reach the sensor.
How to diagnose P0174
Start by reading the fuel trims for both banks with a scan tool. If both banks read high positive trim, look for a shared cause such as a MAF or fuel delivery problem. If only Bank 2 is high, focus on that side and check for a vacuum leak or an exhaust leak near the sensor. Whether the lean condition is worse at idle or across all engine speeds points you to the cause: idle-only usually means a vacuum leak, while lean at all speeds usually means the MAF or fuel supply. The full step-by-step method is the same as the main P0171 guide.
How to fix P0174 and typical cost
Fixes range from free to a few hundred dollars. Tightening a loose hose or clamp costs nothing. A can of MAF cleaner is a few dollars. A replacement MAF or oxygen sensor usually runs about $200 to $600 with labor, and a fuel pump can be $400 to $1,000 or more. Always confirm the repair by clearing the code and watching the fuel trims settle back toward zero on a test drive.
Frequently Asked Questions
Can I drive with a P0174 code?
For a short time, usually yes if the engine runs normally, but fix it soon. A long-term lean condition raises combustion temperatures and can damage the catalytic converter.
Why do I have both P0171 and P0174?
Both lean codes together point to a cause that affects the whole engine, such as a shared vacuum leak, a dirty MAF sensor, or low fuel pressure, rather than a fault on one bank.
What is the most common cause of P0174?
A vacuum or intake leak, followed by a dirty mass air flow sensor. Both let the mixture run lean.