Quick checklist
Check fuel pressure test injectors for leaks clean MAF sensor
OBD2 Codes
P0172 – System Too Rich (Bank 1)
Air/fuel mixture too rich on bank 1; check fuel pressure and injectors.
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Details
The ECM detects rich trims on bank 1. Check fuel pressure injectors and MAF sensor.
Typical causesHigh fuel pressure leaking injector dirty MAF sensor faulty O2 sensor
SymptomsRough idle black smoke from exhaust poor fuel economy
SeverityMedium — can damage catalytic converter
DIY checksCheck fuel pressure test injectors for leaks clean MAF sensor
ToolsFuel pressure gauge OBD2 scanner with live data
Utilities
Copy-paste helpers
Related
Other pages in OBD2 Codes
FAQ
Common questions
Should I replace the O2 sensor first?
No—check fuel pressure and injectors first as they're more common causes.