Fuel and air metering
P0172 — System Too Rich (Bank 1)
The ECU is cutting fuel to correct bank 1 but the mixture still reads rich, meaning there is too much fuel or too little air. It wastes fuel and can foul spark plugs and the catalytic converter.
Common causes
- Leaking or stuck-open fuel injector
- Faulty fuel pressure regulator or high fuel pressure
- Dirty air filter or restricted intake
- Faulty MAF sensor reading too high
- Faulty oxygen sensor or coolant temperature sensor
Symptoms
- Black smoke and fuel smell
- Poor fuel economy
- Rough idle
- Check engine light
How to check
- Check the air filter and the intake path
- Read fuel trims and check the MAF and coolant temperature sensor values
- Test fuel pressure and look for leaking injectors or a bad regulator
- Inspect spark plugs for sooty deposits and check the oxygen sensor
Can you keep driving?
Usually drivable for a short time, but extra fuel can damage the catalytic converter and dilute engine oil. Repair it soon.
Related codes
Frequently asked questions
- What does P0172 mean?
- The ECU sees too much fuel or too little air on bank 1 and cannot fully correct it.
- Can a dirty air filter cause P0172?
- Yes, a badly clogged filter can restrict airflow and enrich the mixture.
General reference information. It does not replace a diagnosis on your own vehicle. The same code can have different causes depending on make, model year and engine; check the manufacturer's documentation or ask a technician with a scan tool.