What P0174 means
The same lean condition as P0171, reported on Bank 2 of a V-configuration engine: unmetered air or under-delivered fuel on that bank, with the computer's correction maxed out. Alone it points at Bank 2's plumbing; paired with P0171 it points at shared systems.
What you’ll notice
- Check engine light
- Rough or surging idle
- Hesitation under light throttle
Likely causes and repair cost
Broad US independent-shop bands, parts and labour.
Can you drive with P0174?
Same as P0171 — drivable, but sustained lean running is hard on the engine's hottest parts. Prompt diagnosis over parts guessing.
The misdiagnosis to avoid
Diagnosing it in isolation when P0171 is also present. Solo P0174 justifies searching Bank 2's gaskets and hoses; the pair means one shared cause, and hunting each bank separately doubles the diagnostic bill for the same hole.
How P0174 actually gets set
The computer targets a specific air-fuel ratio and uses the oxygen sensors to check whether it hit it. When it has to keep adding or subtracting fuel to stay on target, it records that correction as fuel trim. A code sets when the correction exceeds roughly 25% for long enough — meaning the engine is no longer running on its designed mixture and the computer has run out of authority to hide it.
What a scan tool shows that the code does not
Short-term and long-term fuel trim percentages, at idle and at cruise, are the whole diagnosis and none of it is in the code. Trim that is high at idle but normal at higher rpm points at a vacuum leak, because an unmetered air leak matters proportionally less as real airflow rises. Trim that is high across the whole range points at measurement or fuel delivery instead.
The trap with this family of codes
Buying oxygen sensors. The sensor reporting the problem is usually the one part working correctly — it is doing its job by telling you the mixture is wrong. A lean code is far more often a torn intake boot, a cracked vacuum hose, a leaking intake gasket or a dirty mass airflow sensor, and the cheapest of those costs ten dollars to clean.
What happens when you clear it
Fuel trim values reset when the code is cleared and take time to relearn, so clearing immediately before a diagnosis destroys the most useful evidence. Read the trims before anyone clears anything.
A lean condition left running is harder on an engine than a rich one, because it burns hotter. A rich condition wastes fuel and eventually clogs the catalytic converter. Neither is an emergency; neither should be ignored for a year.
Describe what it’s doing in your own words and the symptom checker gives you a safe-to-drive verdict, ranked causes with costs, and notes to take to the shop — free, no sign-up.
A basic code reader costs around $25 and usually pays for itself the first time a warning light comes on. We compare them in choosing an OBD2 scanner.
Questions people ask
Which side of my engine is Bank 2?
The bank not containing cylinder 1 — and where cylinder 1 lives varies by manufacturer. On many V6/V8s Bank 2 is the driver's side but on plenty it isn't; check your engine's layout in service data before buying anything side-specific.
Intake manifold gaskets keep coming up. Why?
On many V-engines the manifold sits between the banks with long gasket runs that harden with heat cycles and leak at the ends first — which shows up as lean codes, sometimes one bank before the other. It's a known pattern on enough engines that shops check it early on lean pairs.