Guide step
Know the baseline
Fuel trim near zero is normal. Large positive or negative corrections point to a root system issue.
Guide page
How to Read Live Fuel Trim Data Without Guessing
Use short-term and long-term fuel trim to separate vacuum leaks, sensor faults, and fuel delivery issues.
Guide step
Compare idle vs cruise
A vacuum leak often looks worse at idle, while fuel delivery issues may show more under load.
Guide step
Cross-check sensors
Always compare trim data with MAF, O2, and coolant readings before replacing parts.