Powertrain
generic / SAE
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.
SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number1 / 72
Possible causes
- Fuel pressure regulator stuck closed high
- Leaking fuel injector medium
- Severely blocked air filter medium
- Oxygen sensor reporting incorrectly low
Symptoms
- Check engine light on
- Increased fuel consumption
- Black smoke from exhaust on acceleration
- Smell of unburned fuel, fouled spark plugs
Inspection / repair
- Difficulty: medium
- DIY: possible
- Estimated cost: 50–600 €
- Estimated time: 0.5–4 h
- Component: fuel pressure regulator
- Component: fuel injector
- Component: air filter
- Component: oxygen sensor upstream
- Component: mass air flow sensor
- MIL / check engine light
- emissions-relevant
- drive cycle required
Sources
References
sae:J2012