P0174
System Too Lean Bank 2
Fuel & air metering
Generic OBD-II
High
What it means
P0174 means the engine control module has detected too much air or too little fuel in the bank 2 cylinders — the mixture is running lean. The most common cause is unmetered air from a vacuum leak or a dirty mass airflow sensor, though weak fuel delivery can also be to blame. A sustained lean mixture raises combustion temperature and can lead to misfires.
High
Can I keep driving? Usually drivable short-term, but a persistently lean mixture raises combustion temperatures and can cause misfires, so diagnose it before long trips.
Common symptoms
What you'll notice
- Check-engine light on
- Rough idle, hesitation, or occasional misfire on acceleration
- Reduced power and sluggish performance
- Slightly worse fuel economy
Common causes
Most likely first
- Vacuum or intake leak letting in unmetered air (most common)Likely
- Dirty or failing mass airflow (MAF) sensorCommon
- Low fuel delivery — clogged filter, weak pump, or low pressureCommon
- Failing upstream oxygen sensor reporting a false lean signalLess often
- Exhaust leak ahead of the O2 sensor pulling in airLess often
- Weak or partially clogged fuel injectors on bank 2Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data, then smoke-test the intake for vacuum leaks — the usual cause.
- Inspect and clean the MAF sensor; check the air intake boot for cracks.
- Check fuel pressure and the fuel filter to rule out lean-from-starvation.
- Review live O2 and fuel-trim data to confirm the bank 2 lean condition.
- Inspect the exhaust manifold and gaskets near the sensor for leaks.
- If trims are still lean, test the injectors. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0174?+
For short trips usually, but don't ignore it — a lean mixture runs hot and can trigger misfires that damage the catalytic converter over time.
Can I just clear P0174?+
It will come back within a drive cycle or two until the vacuum leak, MAF, or fuel-delivery cause is repaired.
Related codes
Often seen with P0174
Read & clear P0174 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX