P0172 – System Too Rich (Bank 1)
Description
The ECM detects a rich air-fuel mixture on Bank 1 based on fuel trim and O2 sensor data. Use the Fuel Trims guide and OBD2 Live Data guide to identify the pattern before replacing parts.
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A diagnostic scanner with live data, freeze-frame information and the right system access can help you investigate the actual cause before replacing parts.
Compare Diagnostic ScannersSymptoms
- Black smoke from exhaust
- Poor fuel economy
- Rough idle
- Fuel smell
- Fouled spark plugs
Causes
- Leaking fuel injector
- High fuel pressure or stuck regulator
- Faulty O2 sensor stuck rich
- Restricted air intake
Diagnosis
- Monitor fuel trims and O2 sensor switching
- Check fuel pressure with gauge
- Inspect injectors for leakage
- Inspect air filter and intake restrictions
Repair
- Repair or replace leaking injectors
- Correct high fuel pressure
- Replace faulty O2 sensor
- Restore proper air intake flow
