Ask Andy AIP0171 System Too Lean (Bank 1)
What it means, what causes it, and what it costs to fix.
What P0171 means
The computer is adding a lot of extra fuel on bank 1 to keep the air-fuel ratio right. It's maxing out its correction (long-term fuel trim, often +25% or more). That means more air is getting in than the computer measured, or less fuel is being delivered than it commanded.
Can I drive with P0171?
Severity: Medium. Fix soon so it doesn't turn into something bigger.
Usually drivable short term, but a lean engine runs hotter and can misfire. Get it checked soon, especially if you also have misfire codes.
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Ask Andy about P0171Symptoms
- Check engine light
- Rough idle, especially when warm
- Hesitation on acceleration
- Possible misfire codes
- Whistling or hissing from the engine bay (vacuum leak)
Common causes
Most likely first.
- Vacuum leak: cracked hose, intake gasket, PCV hose, or brake booster line
- Dirty or failing MAF sensor under-reading airflow
- Weak fuel pump or clogged fuel filter
- Clogged fuel injectors
- Exhaust leak ahead of the front O2 sensor pulling in outside air
How to diagnose P0171
- Check fuel trims in live data. If they're high at idle and drop toward normal at 2,500 rpm, suspect a vacuum leak. If they're high everywhere, suspect fuel delivery or the MAF.
- Smoke-test the intake for vacuum leaks. It's the fastest way to find them.
- Clean the MAF sensor with MAF-safe cleaner and recheck.
- Test fuel pressure and volume.
Tip: most US auto parts stores will read your codes for free.
Repair costs
| Vacuum hose or PCV repair | $20–$300 |
| Intake manifold gasket | $200–$600 installed |
| MAF sensor | $10 cleaning to $350 installed |
| Fuel pump | $400–$1,200 installed |
Typical US prices. Your vehicle, region, and shop rates will change these.
P0171 FAQ
What does P0171 mean?
P0171 means "System Too Lean (Bank 1)." The computer is adding a lot of extra fuel on bank 1 to keep the air-fuel ratio right. It's maxing out its correction (long-term fuel trim, often +25% or more). That means more air is getting in than the computer measured, or less fuel is being delivered than it commanded.
Can I drive with a P0171 code?
Usually drivable short term, but a lean engine runs hotter and can misfire. Get it checked soon, especially if you also have misfire codes.
What is the most common cause of P0171?
The most common cause is: Vacuum leak: cracked hose, intake gasket, PCV hose, or brake booster line. Other causes include dirty or failing maf sensor under-reading airflow and weak fuel pump or clogged fuel filter.
How much does it cost to fix P0171?
Typical repairs run about $10 to $1,200 in the US, depending on the cause. Vacuum hose or PCV repair: $20–$300.
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