P0172: Fuel Trim System Too Rich (Bank 1)
MediumPowertrainFuel System
Symptoms
- Poor fuel economy
- Black smoke from the exhaust
- Strong fuel smell
- Rough idle and fouled spark plugs
Common causes
- Leaking fuel injector dripping into a cylinder
- Faulty or contaminated MAF sensor
- Excessive fuel pressure from a stuck regulator
- Clogged air filter restricting airflow
- Failing upstream oxygen sensor
What to do?
Check fuel trims on a scan tool - long-term trim well below zero confirms a rich condition. Inspect the air filter and MAF sensor, then test fuel pressure. If injectors are suspect, a balance test or current ramp can identify a stuck-open injector.