P0174: System Too Lean (Bank 2)
Same condition as P0171 but on bank 2 of a multi-bank engine (V6, V8, flat-six, etc.). When P0171 and P0174 appear together, the cause is usually a shared component such as the MAF sensor or a central vacuum leak rather than a bank-specific fault.
What P0174 means
P0174 is a generic OBD-II powertrain code in the fuel & air group. In plain English: the engine is getting too much air or too little fuel, and the computer has run out of room to correct it. Bank 2 is the side of a V or flat engine opposite cylinder 1.
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Not typical
- Drive cycle to clear
- Required
Get it fixed
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Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
Common causes
- 01Central vacuum leak (intake manifold gasket, brake booster)Most likely
- 02MAF sensor contaminatedMost likely
- 03Fuel pressure low (affects both banks)Possible
Can I drive with P0174?
Usually yes, for a short time.
The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
Why we rate it moderate
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
- Needs a drive cycle to confirm a repair
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P0174
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P0174. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for P0171. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Read fuel trims and look for leaks
Compare short- and long-term fuel trims at idle and at 2,500 rpm. Trims that drop as rpm rises point to a vacuum leak; trims that stay high point to fuel delivery or a MAF reading low. Smoke-test the intake for leaks.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Central vacuum leak (intake manifold gasket, brake booster); MAF sensor contaminated; fuel pressure low (affects both banks). Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and complete a full drive cycle (cold start, idle, steady highway cruise, deceleration). The code is fixed when the related readiness monitor completes without it returning.
P0174 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Moderate
- Good DIY job?
- Yes, with a scan tool
Needs a scan tool and some experience with testing.
Parts and systems involved
- Intake manifold
- Mass air flow sensor
- Fuel pump
- Fuel pressure regulator
P0174 FAQ
What does P0174 mean?
P0174 means “System Too Lean (Bank 2)”. Same condition as P0171 but on bank 2 of a multi-bank engine (V6, V8, flat-six, etc.). When P0171 and P0174 appear together, the cause is usually a shared component such as the MAF sensor or a central vacuum leak rather than a bank-specific fault.
Is P0174 serious? Can I keep driving?
We rate P0174 as moderate severity. Usually yes, for a short time. The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
What causes P0174?
The most common causes, from most to least likely: Central vacuum leak (intake manifold gasket, brake booster); MAF sensor contaminated; Fuel pressure low (affects both banks). Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P0174?
Typical labor is about $65–$500 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P0174 myself?
DIY difficulty is moderate. Many owners can handle it with a scan tool, a multimeter and basic hand tools. Always confirm the cause before buying parts.
Will P0174 clear itself?
Once the fault is fixed, the check engine light usually goes off by itself after the system passes its self-test over several drive cycles. Clearing the code with a scan tool resets readiness monitors, so an inspection station may turn you away until a full drive cycle is completed.