P0171: System Too Lean (Bank 1)
Can you still drive? Yes, but fix it soon. Running lean can cause engine overheating and damage to pistons and valves over time.
What Does P0171 Mean?
Code P0171 indicates that the engine control module has detected a lean air-fuel mixture on bank 1 of the engine. This means there is too much air or not enough fuel entering the combustion chambers. The ECM tries to compensate by adding fuel, but when the correction exceeds a threshold, the code is set.
Need to read your codes?
An OBD-II scanner lets you read and clear diagnostic trouble codes from your vehicle's computer. Most scanners work with any car made after 1996.
Browse OBD-II Scanners on AmazonCommon Causes
- Vacuum leak in intake manifold
- Faulty mass airflow sensor
- Weak fuel pump
- Clogged fuel filter
- Clogged or restricted fuel injector
Symptoms
- Check engine light on
- Rough idle
- Hesitation during acceleration
- Poor fuel economy
- Engine may stall
Diagnostic Steps
- 1Check short-term and long-term fuel trims with scan tool
- 2Perform smoke test for vacuum leaks
- 3Clean or replace mass airflow sensor
- 4Test fuel pressure at the rail
- 5Inspect PCV valve and hoses
- 6Check for cracked intake boots
Recommended Parts & Tools
mass airflow sensor
fuel injector cleaner
intake manifold gasket set
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $75 - $1200 |
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Chat with AI About P0171Commonly Affected Vehicles
Related Recalls
1 Active Recall — 2026 Ford F-150
The following NHTSA safety recalls have been issued for this vehicle. Contact your dealer to check if your vehicle is affected.
ELECTRICAL SYSTEM: INTEGRATED TRAILER BRAKE CONTROL
Ford Motor Company (Ford) is recalling certain 2021-2026 F-150, 2022-2026 F-250 SD, F-350 SD, F-450 SD, F-550 SD, Maverick, 2024-2026 Ranger, 2023-2026 F-600 SD, 2022-2027 Lincoln Navigator, Expedition, and 2026 E-Transit vehicles. When towing a trailer, the integrated trailer module (ITRM) may lose communication with the vehicle, possibly causing a loss of brake and turn signal lights, or a loss of brake function. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 108, " Lamps, Reflective Devices, and Associated Equipment."
Remedy: The integrated trailer module software will be updated by a dealer, or through an over-the-air (OTA) update, free of charge. Owner notification letters are expected to be mailed March 17, 2026. Owners may contact Ford customer service at 1-866-436-7332. Ford's number for this recall is 26C10. Vehicle Identification Numbers (VINs) involved in this recall will be searchable on NHTSA.gov beginning March 17, 2026.
Data provided by the National Highway Traffic Safety Administration (NHTSA).
Frequently Asked Questions
What does running lean mean?
Running lean means there is too much air or too little fuel in the combustion mixture. The ideal ratio is 14.7 parts air to 1 part fuel.
Can a dirty air filter cause P0171?
A dirty air filter alone rarely causes P0171, but a contaminated mass airflow sensor is a very common cause. Try cleaning the MAF sensor first.
Community Fix Reports
Community reports are user-submitted and not verified by Auto AI Buddy. Results may vary.
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