P0172: System Too Rich (Bank 1)
ECM is subtracting more than -20% fuel trim on Bank 1 due to excess fuel or restricted airflow.
| Trouble Code (DTC) | P0172 |
|---|---|
| Official SAE Definition | System Too Rich (Bank 1) |
| Vehicle Subsystem | powertrain |
| Driving Severity | MEDIUM |
Observable Symptoms
- Increased fuel consumption
- Black exhaust soot or fuel smell
- Rough idle when warm
Most Probable Root Causes
- Leaking fuel injector or excessive fuel rail pressure
- Purge valve (EVAP) stuck open drawing fuel vapors
- Dirty air filter or skewed MAF sensor reading high
Step-by-Step Diagnostic Procedure
- Inspect LTFT/STFT in live data
- Clamp EVAP purge line temporarily to test if fuel trims normalize
- Check fuel injector balance and high-pressure fuel pump seal