What P0174 means
Bank 2 of the engine is running lean: too much air or too little fuel reaches the cylinders on that side. Bank 2 only exists on V and flat engines, and it's the side without cylinder 1. An air leak after the airflow sensor, such as a cracked hose or a leaking intake gasket, is the most common cause.
How the engine computer detects it
With closed-loop control the engine module corrects the injected fuel using the oxygen sensor: short-term fuel trim reacts within fractions of a second, long-term trim stores a learned base correction per load and speed range. Positive values mean fuel is being added because the mixture was lean, negative values mean fuel is being removed; around ±10 % is normal. P0174 is the bank 2 counterpart of P0171 and only exists on V and boxer engines with separate mixture control per bank. The limits match: GM a long-term factor of about 1.30 (engine-specific), Ford above +25 % with short-term trim above +1 %; an older Saab V6 flagged more than 25 % deviation for 20 s. Two trips, no limp mode. P0174 alone points to a leak, injector or exhaust leak on bank 2; together with P0171 to a shared cause such as the air flow sensor, fuel pressure or crankcase ventilation – exactly what several GM bulletins describe. Diagnosis hint: trims very high only at idle and normal under load point to an air leak; trims rising with load point to fuel shortage or an air flow sensor reading low. The oxygen sensor only reports what is in the exhaust and is rarely the cause.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on (after two drive cycles)
- Rough or unsteady idle, possibly stalling
- Hesitation or lack of power when accelerating
- Hissing or whistling from the engine bay (air leak, PCV)
Common causes
- Air leak after the air flow sensor on bank 2 (intake manifold gasket, vacuum hoses, throttle body gasket, brake booster line) Most likely
- Crankcase ventilation leaking or faulty (PCV hose, diaphragm in valve cover, oil cap, dipstick) Most likely
- Air flow sensor dirty or drifting (measures too little air) Possible
- Fuel pressure or delivery too low (weak pump, clogged filter, regulator, tank nearly empty) Possible
- Injectors clogged, or exhaust leak ahead of the oxygen sensor Less likely
How to diagnose P0174
- Check whether P0171 is set too. Both together point to a shared cause like the airflow sensor, fuel pressure or crankcase ventilation. P0174 alone points to a leak on the bank 2 side.
- Make sure the oil filler cap and dipstick are seated, and listen at idle for hissing around the intake and the PCV hoses.
- On a scanner, compare fuel trims at idle and at 2,500 rpm. High only at idle suggests a vacuum leak; worse under load suggests a fuel supply or airflow sensor problem.
- Ask a shop for a smoke test of the intake. It finds intake gasket leaks you can't see or hear.
- Check for an exhaust leak ahead of the bank 2 front oxygen sensor, which lets in air and makes the mixture read lean.
Vehicles that report P0174 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Ford Windstar | 1999–2003 | 19 | 82k | |
| Buick Enclave | 2008 | 3 | — | |
| Toyota Highlander | 2017–2019 | 3 | — |
Counts of owner complaints to the NHTSA that mention P0174 (59 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 1
- Fuel and air metering
- 74
- Specific fault
Questions drivers ask
Can I drive with code P0174?
Yes, for now, if the engine runs smoothly. It may idle rough or hesitate, and over time a lean engine can misfire and run hotter, so get it checked soon. Stop driving if the check engine light starts flashing.
Will my car pass an emissions inspection with P0174?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0174 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0174 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0174. They can point to a shared cause, so it's worth checking them together.
- P0171System Too Lean Bank 152 complaints
- P0300Random/Multiple Cylinder Misfire Detected8 complaints
- C1185Manufacturer-specific code3 complaints
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.