Fault-Code Library · Fuel mixture
P0172: System too rich, bank 1
Fuel trim has reached a rich threshold because the ECU is removing more fuel than expected.
Common symptoms
- •Fuel smell
- •Poor economy
- •Sooty tailpipe
- •Rough idle
Likely causes
- •Leaking injector
- •Incorrect airflow reading
- •High fuel pressure
- •Failed purge valve or rich EVAP flow
First checks
- •Review short- and long-term fuel trims
- •Check fuel pressure and injector leak-down
- •Inspect purge valve operation and MAF plausibility
Important
Driving with a rich mixture can damage catalysts and dilute engine oil.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.
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