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Diagnosis for P0171
Contextualized for 2018 Honda Civic
monitor & address
P0171
System Too Lean (Bank 1)
The engine is running lean on bank 1.
SEVERITYwarn
DIY Feasibility
Moderate if the leak is obvious; otherwise diagnostics first.
Est. Repair Cost
$80-$650
Vehicle Context
2018 Honda
Likely causes
- 01Vacuum leak after the mass air flow sensor
- 02Dirty or misreading MAF sensor
- 03Weak fuel pump or clogged fuel filter
- 04PCV or intake boot leak
First checks
- 01Look at short-term and long-term fuel trims.
- 02Smoke test the intake and PCV system.
- 03Inspect the air filter box, ducting, and MAF wiring.
Common fixes
- Clean or replace the MAF sensor
- Repair vacuum leaks
- Verify fuel pressure before replacing parts