P0171: System Too Lean Bank 1
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Driveable short-term, but a lean engine runs hot - prolonged driving risks misfires and converter damage. Diagnose within a couple of weeks.
Symptoms
- Rough idle, especially cold
- Hesitation or surging at cruise
- Occasional stalling at stops
- Hissing sound from the engine bay (vacuum leak)
Likely causes, most common first
- Vacuum leak - cracked hose, intake gasket, PCV parts (most common)
- Dirty mass airflow sensor under-reporting air
- Weak fuel pump or clogged filter starving the engine
- Leaking or stuck-open EGR or purge valve
Read P0171 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0171 means bank 1 is running lean: the computer keeps adding fuel beyond its normal authority to hold the correct air-fuel ratio. Either unmetered air is sneaking in past the airflow sensor, or fuel delivery cannot keep up.
The classic culprit is a vacuum leak after the MAF sensor - hoses get brittle, intake gaskets shrink. A smoke test finds these quickly. Fuel trim data tells the story: lean at idle but normal at speed points to a vacuum leak; lean everywhere points to fuel supply or MAF. On four-cylinder engines P0171 stands alone; a V engine lean on both banks (P0171 + P0174) almost always has a shared cause - MAF or fuel pressure.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0171
“Exhaust bracket broke, created a hole in pipe, which then resulted in cracked catalytic converter. Dealership and GM denied repairs due to the hole being on the "wrong pipe" but the same bracket that is covered broke resulting in the consequential damage. Check engine light came on, loud exhaust noise. Threw codes P219A, P2097, P0171. Bulletin even outlines that broken bracket/hole can cause cracks in converter, still denied. This is a known issue with the welding on this pipe/bracket, why they didn't extend the coverage to BOTH pipes is beyond me.”2019 Chevrolet Traverse · Apr 2026
“Vehicle hesitates and sputters upon acceleration, loss of power, and stalls during operation. Trouble codes P0191, P0171, P0174, and P0107B have generated in combination.”2019 Toyota Highlander · Mar 2026
“Issue: Some 2021-2023 F-150 vehicles equipped with a 3.3L engine may exhibit an illuminated MIL in the instrument panel cluster (IPC) with OTC P0171 stored in the powertrain control module (PCM). This may be due to the software level of the PCM. To correct this issue, follow the Service Procedure to reprogram the PCM to the latest software level using the Ford Diagnosis and Repair System (FORS). Description: 2021-2023 F-150 3.3L: Reprogram The Appropriate Modules As Required By The Software Update And Service Procedure (Do Not Use With Any Other Labbr Operations) Ford has current recalls for this issue but my vehicle was not included.”2022 Ford F-150 · Apr 2025
Show 7 more owner reports
“Rough idle on start. RPM is not maintaining to keep the engine running. After a few try, it starts ok and drive off the parking lot, but the engine dies after about 10 seconds over 30mph. It feels like gasoline is not igniting corretly. Scanned Error Code P0171: System Too Lean Bank 1 P0190: Fuel Rail Pressure Sensor A Circuit Dealership can't replicate the issue and find the issue. Could be related to Fuel System Recall.”2019 Volkswagen GTI · Sep 2024
“I was driving home from work when I felt my car was in a limp like a previous problem I had except this time I had a check engine light come on. I was almost home and I had a check hybrid system pop up on my dash and the car basically stopped driving. Luckily I was on a side street. I had a p0171 code on both of my issues . I had it fixed about a month and half ago the first time but couldn't say what caused the issue.”2023 Kia Sorento · Jun 2024
“Ongoing issues with rough idle. Threw a couple generic lean codes (p0171 and p0174) that did not stay. Stored code p061a:00-28. On my third dealer. Vehicle randomly shut off at stop sign with no codes thrown whatsoever. Tech believes the issue is the throttlebody. Ford Corp says it passes their tests and will not warranty the replacement. Ford Corp Basically said I have to wait till total part failure. Shutting off in traffic is obviously dangerous.”2023 Ford Mustang · May 2024
“Multiple reports of; Codes P0171 System too lean bank 1 P0138 O2 sensor circuit high (b1s2) P0087 Fuel pressure too low P0036 B1S2 *** frequent fuel pump and fuel injector replacements/ services due to defects in the system. Causing major damage in other systems including engine.***”2014 Kia Sorento · Mar 2024
“While driving 60 MPH on the highway my car started stuttering then lost all power. It threw 3 codes P0131, P2097 and P0171. I have spent over $1,000.00 and a month later they tell me it was my intake bolts that were loose. They replaced every part PCV valve, MAF sensor, O2 sensor and car still wouldn't run right. PLEASE address this issue as that is UNSAFE for a car to just stop on the highway.”2014 Chevrolet Malibu · Mar 2024 · 167,611 mi
“I purchased this F150 in November, 2023. The only code shown was a lean code, P0171. I removed the bed first to begin my inspection. Upon removing the original fuel tank, I discovered a gash in the top of the tank,about 1/8" wide by 3" long. It should have set a code like a missing gas cap would, but there was none. The gash appeared to be several years old due to the rust pitting. I believe the gash was a result of the cross member rubbing against the tank. The previous owner did not mention the defect. Fuel would have spilled out if the tank was completely filled. I did not find any service alerts for this though they may exist. The truck currently has 225k miles.”2003 Ford F-150 · Jan 2024
“The Blazer is showing many codes in the ECM, even though it seems to be running properly. The codes include: p0171, p0174, p0101, p0128, p0155, p0300, p1870, p0128, p0155. The dash recently showed warning lights for parking brake, ABS, and Service Engine soon. It was checked a few days ago by a local repair shop. Two previous recalls showed multifunction switch failures which affected many vehicles.”2002 Chevrolet Blazer · Oct 2023
Cars that report P0171 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0171?
Driveable short-term, but a lean engine runs hot - prolonged driving risks misfires and converter damage. Diagnose within a couple of weeks.
How much does it cost to fix P0171?
Typical US repair costs range from $20 for the simplest fix (maf sensor cleaning) to $1,000 in the worst case. The right number depends on which cause your car has - see the causes list.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.