Answer
Dec 31, 2025 - 02:50 AM
P0171 and P0174 together on a Hyundai Azera (2006-2012) mean the engine’s running lean on both banks. In plain terms: the ECU thinks it’s not getting enough fuel (or it’s getting too much air).
When both banks throw lean codes at the same time, I usually look at things that affect the whole engine, not just one side.
Common causes on these Azeras:
- Vacuum leak — Biggest suspect. Cracked vacuum hoses, PCV hose split, intake boot leaking, or intake manifold gasket starting to leak. These get worse when warm.
- MAF sensor dirty or failing — If the MAF under-reports airflow, the ECU doesn’t add enough fuel. Very common. Pull it and clean it properly with MAF cleaner, not brake cleaner.
- Unmetered air after the MAF — Any air getting in downstream of the MAF will lean out both banks. Check the intake duct for cracks you can’t see until you flex it.
- Low fuel pressure — Weak pump, clogged filter, or a tired fuel pressure regulator. Since both banks are lean, fuel delivery is a real possibility. Needs a gauge to be sure.
- Exhaust leak before the O2 sensors — A leak upstream can pull in air and trick the sensors into thinking it’s lean.
- Bad upstream O2 sensors (less common) — Possible, but I don’t jump to sensors first when both banks set lean. They usually don’t fail together unless the mileage is high.
How I’d attack it:
- Smoke test or spray test for vacuum leaks
- Clean and check the MAF
- Check fuel pressure hot and cold
- Look at live data (LTFT/STFT) — if trims drop when you rev it, that screams vacuum leak
Fortunately, this 2006–2012 Hyundai Azera manual goes through this step by step — vacuum diagrams, fuel pressure specs, MAF values, and diagnostic flow charts so you’re not guessing.
Wish you the best of luck!
