P0174: System Too Lean (Bank 2)

P0174 means the engine is running too lean on Bank 2, the cylinder bank that does not contain cylinder 1, so this code only appears on V6, V8, and boxer engines. The computer added the maximum extra fuel it can (long-term fuel trim past roughly +25 percent) but still measured too much air against the ideal 14.7:1 ratio. The most common cause is an unmetered air leak: a cracked vacuum hose or leaking gasket. Most repairs cost under 100 euros.

P0174 is a fuel system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0174 and illuminates the check engine light.

If your vehicle has triggered P0174, you may notice one or more of these symptoms:

• Check engine light illuminated, sometimes flashing under load
• Rough, high, or unstable idle
• Hesitation or stumble during acceleration
• Reduced fuel economy
• Engine may stall at idle or when coming to a stop
• Hissing or whistling sound from a vacuum leak
• Slight loss of power and occasional misfire

Here are the most common causes of P0174, ranked by how likely they are to be the culprit:

Generally yes, for short-term driving. Short-term driving is safe. Avoid heavy load and high RPM. A lean condition increases combustion temperatures and can damage catalytic converters and exhaust valves if left unaddressed. Fix within a couple of weeks.

Follow these steps to pinpoint the root cause of P0174:

1. Check whether P0171 is also stored. Both codes together points to a whole-engine cause (dirty MAF, low fuel pressure, or a large central vacuum leak), not a Bank 2-specific fault, so start there
2. Read short-term and long-term fuel trims on Bank 2 with a scan tool. A long-term trim above roughly +15 percent confirms the bank is running lean; trims that worsen at idle suggest a vacuum leak, trims that worsen under load suggest a fuel-delivery problem
3. Smoke-test the intake, or spray a small amount of carburettor cleaner around the Bank 2 intake manifold gaskets, vacuum hoses, and PCV connections, watching for an RPM change that pinpoints the leak
4. Inspect and clean the MAF sensor with dedicated MAF cleaner, then recheck trims; a clogged sensor element is a frequent and cheap fix
5. Check fuel pressure at the rail with a gauge and compare against the manufacturer specification, both at idle and under a snap-throttle load
6. Inspect for an exhaust leak ahead of the Bank 2 upstream O2 sensor and verify the sensor is switching correctly before condemning any parts
7. Compare Bank 1 and Bank 2 trims side by side - a large gap between the two banks isolates the problem to Bank 2 hardware rather than a shared cause

Repair costs for P0174 vary depending on the root cause and your vehicle. Here are typical estimates:

P0174 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P0174 or indicate related issues: