Last reported case: 3 weeks ago
Based on 3 owner reports (1 from Reddit, 2 from forums)
What is P0171?
P0171 indicates your engine's Bank 1 is running with too much air and not enough fuel, which is called a 'lean' condition. This is a medium-severity powertrain issue that can reduce fuel economy and performance, and it's commonly triggered by vacuum leaks or faulty sensors. Based on 551 reports, repairs for this code average $4596, with Ford Mustangs and F-150s being among the most frequently affected vehicles.
Common Causes:
- Vacuum leaks in intake hoses or gaskets (reported in numerous discussion clusters)
- Faulty mass airflow (MAF) or oxygen (O2) sensors
- Clogged or failing fuel injectors
- Fuel delivery issues like a weak fuel pump or clogged filter
Symptoms:
- Check Engine Light is illuminated
- Reduced engine power or hesitation during acceleration
- Poor fuel economy
- Rough idle or engine misfires
🚗P0171 on 2020 FORD Mustang
This page focuses specifically on P0171 issues reported by 2020 FORD Mustang owners. The experiences and fixes below are from real owners of this exact vehicle.
Symptoms Reported by 2020 FORD Mustang Owners:
Parts Often Involved:
What Owners Say
Real experiences from 2020 FORD Mustang owners
“My car has 120k miles and also has an offroad x pipe. I have also noticed my gas mileage has dropped dramatically (10mpg sometimes) I'm just looking for some more input before I go out and replace the sensor.”View original
“It's reading lean so the ecu is dumping more gas in. It could also be a loose exhaust manifold but it's unlikely because the stock studs aren't known for loosening up.”View original
“It could also be a loose exhaust manifold but it's unlikely because the stock studs aren't known for loosening up. P0171 is only for one cylinder bank, a defective maf would affect both.”View original
“I have also noticed my gas mileage has dropped dramatically (10mpg sometimes) I'm just looking for some more input before I go out and replace the sensor.”View original
These are real experiences shared by 2020 FORD Mustang owners on automotive forums and communities. Results may vary based on vehicle condition and repair quality.
About This Data
This page aggregates 3 discussions about P0171 from 2020 FORD Mustang owners across automotive communities.
Success rate (0%) is calculated from posts where owners confirmed whether their fix resolved the issue.
Last updated: 2/12/2026