P0172 — System Too Rich (Bank 1)
Moderate severityWhat it means
The air–fuel mixture on bank 1 contains too much fuel, and the engine control unit is removing as much fuel as it is allowed to. A rich mixture wastes fuel, fouls spark plugs and can damage the catalytic converter.
Common symptoms
- Black smoke from the exhaust
- Strong fuel smell
- Rough idle and fouled spark plugs
- Noticeably higher fuel consumption
Likely causes
- Leaking or stuck-open fuel injectors
- Excessive fuel pressure (faulty regulator)
- Dirty MAF sensor over-reporting airflow
- Stuck-open EVAP purge valve
- Faulty coolant temperature sensor keeping the engine in cold-start enrichment
What to check first
- Watch long-term fuel trims in live data — values far below −10% confirm a rich condition
- Check the coolant temperature reading for plausibility
- Inspect and clean the MAF sensor
- Test fuel pressure and the purge valve
Can you keep driving?
Drivable for short distances, but running rich fouls plugs and can overheat the catalytic converter — repair soon.
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