OBD-II code · Powertrain (generic)
P0172 System Too Rich (Bank 1)
Long-term fuel trim on bank 1 is at the lower limit — the ECU is removing fuel from baseline but mixture remains too rich. Indicates excess fuel delivery, restricted air flow, or a faulty oxygen sensor reporting falsely lean.
Is it safe to drive with P0172?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyFuel pressure regulator stuck closed
- PossibleLeaking fuel injector
- PossibleSeverely blocked air filter
- Less likelyOxygen sensor reporting incorrectly
Symptoms
- Check engine light on
- Increased fuel consumption
- Black smoke from exhaust on acceleration
- Smell of unburned fuel, fouled spark plugs
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.5–4 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Fuel Pressure Regulator, Fuel Injector, Air Filter, Oxygen Sensor Upstream, Mass Air Flow Sensor
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.