P0174 System too lean (bank 2)
What P0174 means
The engine computer has had to add fuel on bank 2 as far as it is allowed and the mixture is still too lean. A lean mixture burns hotter, which can cause misfires and, over time, damage valves and the catalytic converter. Bank 2 is the side of a V6, V8 or boxer engine that does not contain cylinder 1.
P0174 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.
At a glance
- Severity
- High
- Typical repair cost
- 50–600 €
- Workshop time
- 0.5–4 h
- Repair difficulty
- Medium
- DIY possible
- Yes
- Check engine light
- Yes
- Affects emissions test
- Yes
Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold starts
- Power loss under load
Common causes
- Vacuum leak (intake gasket, PCV hose, brake servo hose)
- Dirty or faulty mass air flow sensor under-reading airflow
- Low fuel pressure from a weak pump or clogged filter
- Clogged injectors on bank 2
- Exhaust leak before the bank 2 oxygen sensor
Can I keep driving with P0174?
Get it to a workshop within a few days. Long-term lean running burns hotter and can damage valves and the catalytic converter.
What to check first
- Check whether P0171 (bank 1 lean) is also stored: both banks lean points to a shared cause such as the MAF, fuel pressure or a central vacuum leak.
- Smoke-test the intake and listen for hissing around hoses and the intake manifold.
- Clean or test the MAF sensor and check fuel pressure and the fuel filter.
- If only bank 2 is lean, check that side's intake gasket, injectors and exhaust manifold.
Related codes
- P0173 Fuel trim malfunction (bank 2)
- P0175 System too rich (bank 2)
- P0172 System too rich (bank 1)
- P0171 System too lean (bank 1)
- P0170 Fuel trim malfunction (bank 1)
- P0181 Fuel temperature sensor A range/performance
- P0161 Oxygen sensor heater circuit (bank 2, sensor 2)
- P0160 Oxygen sensor circuit no activity detected (bank 2, sensor 2)
Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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