P0172
Medium SeveritySystem Too Rich (Bank 1)
Fuel System
What Does P0172 Mean?
Bank 1 is running rich — too much fuel relative to air. The ECM cannot trim enough fuel out to compensate.
Common Fix
Replace leaking injector or fuel pressure regulator
Estimated Cost (DIY)
$30 - $200
Symptoms
- ⚠️Black exhaust smoke
- ⚠️Strong fuel smell
- ⚠️Poor fuel economy
- ⚠️Fouled spark plugs
Common Causes
Leaking fuel injectorlikely
Faulty O2 sensor reading leanpossible
High fuel pressure (bad regulator)possible
Dirty air filter restricting airflowpossible
How to Diagnose P0172
- 1Check fuel pressure
- 2Inspect fuel injectors for leaks
- 3Check O2 sensor operation
- 4Inspect air filter
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Frequently Asked Questions
- Is P0172 dangerous?
- Running rich wastes fuel and can damage the catalytic converter with unburned fuel. Fix within a week.
- Can a dirty air filter cause P0172?
- Yes — a severely clogged air filter restricts airflow, making the mixture rich. Check your air filter first.