What Does P0172 Mean on Your 2021 Ford Bronco Sport?
If your 2021 Ford Bronco Sport has set a P0172 code, the engine control module is detecting that Bank 1 is running too rich. The 2021 Bronco Sport comes with two engine choices: the base 1.5L EcoBoost turbocharged three-cylinder making 181 horsepower, or the 2.0L EcoBoost turbocharged four-cylinder producing 250 horsepower in the Badlands and First Edition trims. Both are inline engines with only one bank.
A rich condition means excess fuel relative to air in the combustion process. This causes poor fuel economy, spark plug fouling, and potential catalytic converter damage if left unaddressed.
Common Symptoms You May Notice
- Check engine light on
- Noticeably worse gas mileage
- Rough or unsteady idle
- Black exhaust smoke
- Gasoline smell from the tailpipe
- Hesitation or stumble during acceleration
Top Causes of P0172 on the 2021 Bronco Sport
- Dirty MAF sensor - The mass airflow sensor gets contaminated by dust and debris, especially on Bronco Sports used for light off-roading or driven on gravel roads. A dirty MAF underreports airflow, leading to excess fueling.
- Boost or intake leak - Both EcoBoost engines have turbo charge piping that can develop leaks at hose connections or the intercooler. Air escaping after the MAF sensor throws off fuel calculations.
- Faulty upstream oxygen sensor - A sluggish O2 sensor feeds incorrect data to the ECM, causing it to add more fuel than needed.
- Stuck-open EVAP purge valve - A purge valve that stays open sends a continuous stream of fuel vapor into the intake manifold, enriching the mixture.
How to Diagnose the Problem
Use an OBD-II scanner to pull codes and freeze frame data. Check STFT and LTFT values. Negative LTFT beyond -10% confirms the rich condition.
Start by checking and replacing the air filter if dirty. Clean the MAF sensor with proper MAF sensor cleaner. On the Bronco Sport, the MAF is in the air intake tube between the filter box and the turbo inlet.
Inspect all turbo charge pipes and intercooler hoses for loose clamps or cracks. The 1.5L three-cylinder has a relatively simple charge pipe layout, making inspection easier.
Monitor the upstream O2 sensor with live data. It should oscillate between 0.1V and 0.9V. Check the EVAP purge valve by testing for vacuum at idle when it should be closed.
Repair Options and Cost Estimates
- MAF sensor cleaning or replacement: Cleaning is under $10. New sensor costs $50-$160 plus $45-$95 labor.
- Boost leak repair: Hoses and clamps run $20-$70. Labor is $70-$170.
- O2 sensor replacement: Parts cost $50-$145. Labor is $70-$135.
- EVAP purge valve replacement: Parts are $25-$60. Labor runs $50-$105.
Can You Fix This Yourself?
MAF cleaning is very easy and takes about 15 minutes. Boost hose checks and tightening are simple. O2 sensor replacement is moderate difficulty. EVAP purge valve replacement is usually straightforward since the valve is accessible on top of the engine.
Prevention Tips
- Replace the air filter more often if you drive on unpaved roads
- Check boost hose connections periodically
- Use quality fuel to minimize fuel system deposits
- Add fuel system cleaner to the tank every 5,000 miles