P0172
PowertrainFuel Systemhigh severitySystem Too Rich Bank 1
What P0172 Means
The long-term fuel trim for Bank 1 has exceeded the negative limit, indicating the engine is running rich. The PCM is subtracting fuel to compensate.
Symptoms
- Check Engine Light
- Black exhaust smoke
- Poor fuel economy
- Rough idle
- Fuel smell
- Fouled spark plugs
Common Causes
- Leaking fuel injector
- High fuel pressure
- Faulty O2 sensor reading lean
- Stuck-open EVAP purge valve
- Saturated charcoal canister
- Faulty MAF sensor (underreporting)
Diagnostic Steps
- Check fuel trim values
- Test fuel pressure
- Check for leaking injectors (fuel pressure drop test)
- Inspect EVAP purge valve
- Test MAF sensor
- Inspect spark plugs
Where to start: Check fuel injectors for leaks. Test fuel pressure regulator. Inspect EVAP system.
🔌 Don't have a code reader?
Any of these will read and clear this code — pick by how deep you want to go.
Budget handheld~$40
ANCEL AD410 →
No-phone-needed handheld — reads, clears, live data, freeze frame.
✓ ANCEL official store
Serious DIY~$100
BlueDriver Pro →
Enhanced codes (ABS, airbag, TPMS) plus repair reports.
SHOP FAVORITEShop-grade tablet~$300
Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
✓ Autel official store
Pro diagnostics$1,500+
Autel MaxiSys MS906 Pro →
Full-system pro platform — topology mapping, ECU coding, the works.
✓ Autel official store
As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.
Related Codes
Community Confirmed Fixes
No confirmed fixes yet for this code. Be the first to contribute!
Submit a FixFound a Fix for P0172?
Help other technicians by sharing what worked on your vehicle.
Submit Your Fix