Your check engine light just came on, and the code reader says P0171. Don’t panic—this is one of the most common codes you’ll see on Honda vehicles. While it sounds technical, figuring out what’s wrong is more straightforward than you think. We’ll walk you through what Honda P0171 actually means, what’s likely broken, and how to get your car running right again without emptying your wallet.
What Does Honda P0171 Actually Mean?
Honda P0171 is the code for “System Too Lean (Bank 1).” In plain English, your engine’s getting too much air or not enough fuel. Your car’s computer expects a specific air-to-fuel ratio—about 14.7 parts air to 1 part fuel. When that balance tips too far toward air, the engine control unit (ECU) tries to fix it by adding more fuel.
The ECU monitors this balance constantly using oxygen sensors and makes tiny adjustments called “fuel trims.” When those adjustments reach 25% or more, the computer throws in the towel and triggers P0171.
On Honda inline-four engines (like most Civics, Accords, and CR-Vs), “Bank 1” just means the whole engine. On V6 models (Pilot, Odyssey, Ridgeline), it’s the rear cylinder bank near the firewall.
Why Your Honda Is Running Lean
The root cause is almost always one of two things: extra air sneaking in where it shouldn’t, or not enough fuel making it to the engine.
Air Leaks Are Enemy Number One
If you drive a 2007-2011 CR-V or 2008-2012 Accord, there’s about an 80% chance your problem is a cracked air intake boot. This rubber hose connects your air filter to the throttle body. Over time, heat and engine movement cause it to crack—usually in those accordion folds.
Here’s the tricky part: these cracks can be tiny. You might not even see them during a quick inspection. They open up when the engine’s running and sucking in air, then close when it’s off.
Other common leak spots include:
- Intake manifold gaskets (especially on V6 engines)
- PCV (Positive Crankcase Ventilation) valve stuck open
- Vacuum hoses that have gone brittle
- Throttle body gasket
Dirty or Failing Sensors
Your Mass Air Flow (MAF) sensor tells the computer how much air is entering the engine. When it gets dirty—usually from oil on aftermarket air filters—it can’t do its job properly. The sensor reports less air than what’s actually flowing in, so the ECU doesn’t add enough fuel.
The oxygen sensor can also cause problems if it’s “lazy” or poisoned by oil or coolant. A failing sensor might tell the ECU the mixture’s too rich when it’s actually fine, causing the computer to cut back on fuel and create a lean condition.
Fuel Delivery Problems
Sometimes the issue isn’t extra air—it’s not enough gas. Your fuel pump might be wearing out, especially if you’ve got high mileage. Honda issued Recall P3W for certain 2015-2019 models where fuel pump failures were common.
If you drive a 2015-2016 Fit or 2017-2018 CR-V with the 1.5L engine, pay attention. Honda extended the warranty on fuel injectors for these models to 10 years or 150,000 miles because of widespread failures. Clogged or failing injectors can’t deliver enough fuel, triggering P0171 along with misfire codes.
How to Diagnose Honda P0171
You don’t need a degree in automotive engineering to track this down. Here’s how pros do it.
Check Your Fuel Trim Numbers
Connect an OBD-II scanner that shows live data. Look at your Short-Term Fuel Trim (STFT) and Long-Term Fuel Trim (LTFT). If they’re both positive and add up to more than 20-25%, you’ve confirmed the lean condition.
Now rev the engine to about 3,000 RPM and watch what happens:
- Fuel trim drops toward 0%: You’ve got a vacuum leak. At idle, the leak represents a huge percentage of total airflow. At higher RPM, it becomes insignificant.
- Fuel trim stays high or increases: Your problem is fuel delivery or a dirty MAF sensor. The pump can’t keep up when demand increases.
| What You See | What It Means | Where to Look |
|---|---|---|
| High trim at idle, normal at 3,000 RPM | Vacuum leak | Intake boot, manifold gaskets, PCV valve |
| High trim at all RPM | Fuel system issue | Fuel pump, injectors, MAF sensor |
| Trim normal but code persists | Sensor problem | Oxygen sensor, MAF sensor |
Visual Inspection Comes First
Pop your hood and squeeze every vacuum hose you can reach. Brittle hoses will crack under light pressure. Check the air intake boot—especially if you have a K-series or L-series engine. Shine a flashlight on it while someone revs the engine. Sometimes you’ll see cracks opening up.
Pull out your air filter. If it’s an oiled aftermarket filter, you might see oil residue near the MAF sensor. That’s your smoking gun.
The Smoke Test
If you can’t find an obvious leak, a smoke machine is worth the investment (or the shop fee). A tech pressurizes your intake system with smoke while the engine’s off. Smoke pouring out of a crack you couldn’t see before makes diagnosis dead simple.
Model-Specific Issues to Know
Different Honda models have their quirks.
CR-V and Accord (2007-2012)
The air intake hose failure is so common on these models that you should replace it preventively if you’re buying a used one. The part costs $90-$180 at a dealer, less if you order aftermarket.
Civic and Fit (2015-2020)
For the Fit specifically, check Technical Service Bulletin 22-002. If you’ve got the 1.5L turbo engine and you’re seeing P0171 with misfires, your injectors are probably done. The extended warranty should cover this.
Pilot, Odyssey, Ridgeline (V6 Models)
V6 engines have more complex intake manifolds with more gaskets to fail. The intake plenum gaskets are a weak point. You’ll also want to check the Variable Cylinder Management (VCM) system vacuum lines.
What It’ll Cost to Fix
Here’s the reality check on repair costs.
| Problem | DIY Cost | Shop Cost (Accord/Civic) | Shop Cost (CR-V/Pilot) |
|---|---|---|---|
| Clean MAF sensor | $10-$20 | $50-$80 | $50-$80 |
| Replace air intake boot | $60-$100 | $150-$220 | $180-$280 |
| New oxygen sensor | $80-$150 | $250-$450 | $350-$700 |
| Replace fuel pump | $200-$400 | $500-$850 | $600-$1,100 |
| Intake manifold gaskets | $80-$150 | $350-$600 | $500-$800 |
| Fuel injector set | $300-$600 | $1,200-$1,600 | $1,400-$1,900 |
Don’t fall into the “parts cannon” trap. We’ve seen people spend $600 replacing sensors when the actual problem was a cracked $15 PCV valve. Get a proper diagnosis before you start buying parts.
Simple Fixes You Can Try First
Before you spend serious money, try these.
Clean Your MAF Sensor
Buy a can of MAF sensor cleaner (not regular electronics cleaner). Remove the sensor—usually held by two screws—and spray the tiny wire elements. Let it dry completely before reinstalling. This fixes the problem about 30% of the time.
Check Your Air Filter
A clogged air filter won’t usually cause P0171, but if you’ve got an oiled aftermarket filter, swap it for a stock paper filter temporarily. If the code clears, you’ve found your culprit.
Inspect the Obvious
Tighten your gas cap. Check every vacuum line you can see. Look for cracks in the intake boot. These take 10 minutes and cost nothing.
When You Absolutely Need a Mechanic
Some repairs aren’t DIY-friendly. Replacing intake manifold gaskets on a V6 requires removing the entire upper intake assembly. Fuel pump replacement means dropping the gas tank. Injector replacement on direct-injection engines involves high-pressure fuel lines that require special tools.
If you’ve tried the simple stuff and the code keeps coming back, it’s time for professional diagnosis. A good independent Honda specialist will charge $100-$150 for diagnosis and save you from throwing parts at the problem.
Why You Shouldn’t Ignore P0171
Running lean isn’t just about a check engine light. Your engine’s combustion temperatures are higher than they should be. Over time, this can damage your catalytic converter—a $1,500-$2,500 part on modern Hondas with ULEV emissions systems.
You might also notice:
- Rough idle or hesitation
- Loss of power under acceleration
- Worse fuel economy (ironically, even though you’re “lean”)
- Engine knock or ping
Prevention Beats Repairs
Once you’ve fixed your P0171, keep it from coming back.
Use quality air filters—stick with OEM paper filters unless you’re committed to maintaining an oiled filter properly. Top Tier gas helps prevent injector clogging on direct-injection engines.
If you’re at 100,000 miles or more, have your valve clearances checked. Tight valves can throw off manifold vacuum readings and cause weird fuel trim issues that are hard to diagnose.
Replace rubber intake components before they fail. That $100 intake boot replacement is cheaper than the diagnostic time you’ll pay later.
The Bottom Line
Honda P0171 looks scary on paper, but it’s usually one of a handful of common issues. Start with the cheap and easy fixes—clean your MAF sensor, inspect for obvious leaks, check that intake boot. If those don’t work, use the fuel trim test to narrow down whether you’re chasing an air leak or a fuel problem.
Don’t rush to the parts store and start replacing sensors. Get the right diagnosis, fix the actual problem, and your Honda will go back to being the reliable machine it’s supposed to be. Most P0171 fixes cost well under $500 if you catch them early and don’t let someone talk you into unnecessary repairs.
