OBD-II · Engine and powertrain (P)
P0172
System too rich bank 1
What it means
Bank 1 is running with too much fuel or not enough air.
Symptoms
- engine warning light
- higher fuel consumption
- fuel smell from the exhaust, possibly black soot at the tailpipe
- rough idle or misfire in severe cases
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | EVAP purge valve stuck open |
| 02 | leaking injector |
| 03 | MAF sensor over-reading |
| 04 | fuel-diluted engine oil after many short trips |
| 05 | coolant temperature sensor reading too cold |
| 06 | high fuel pressure |
| 07 | blocked air filter |
What to check, step by step
- 01Read short- and long-term fuel trims to confirm the ECU is pulling fuel
- 02Temporarily isolate purge flow using the OEM procedure and observe fuel trims; if disconnecting the line, seal the intake connection so the test does not introduce a vacuum leak.
- 03Check the engine oil for fuel dilution (fuel smell, rising level), common after many short trips
- 04Check the coolant temperature reading against the real engine temperature: a sensor reading cold makes the ECU add fuel
- 05Check the air filter, MAF reading and fuel pressure
- 06Leak-test or balance-test the injectors