Positive fuel trim = ECU adding fuel → lean condition. Negative fuel trim = ECU removing fuel → rich condition. But don’t stop there. Check: • Idle vs load • Short-term vs long-term • O₂ switching speed • Maf sensor readings • Coolant temp sensor readings Pattern > single number. There’s always a reason for erratic readings. More deep dives inside AutoTechTools. 📘 https://autotechtools.ca 👥 https://www.skool.com/vehicle-repair-4221/about?ref=7b47cfbaf93a43b59eb7d155812f7013 Fuel trims ever confuse you?

If you’re an apprentice, student, or working tech who wants to get better in the shop and pass your certification exams, you’re in the right place. AutoTechTools was built by a working, certified technician — not a textbook company — to bridge the gap between: - What exams test - And what actually happens on the shop floor This community is about thinking like a technician, not memorizing answers. What you’ll get here: - Real-world diagnostic logic that applies in the bay - Certification-style practice questions (Red Seal / ASE-style thinking) - Clear explanations of why an answer is right or wrong - Exam strategies, common traps, and how to stay calm under pressure - A place to ask questions without ego or judgement Whether you’re: - Writing Red Seal in Canada - Studying for ASE in the U.S. - Or just trying to be sharper, faster, and more confident at work This group is here to support you. 📘 Exam prep guides, practice exams, and bundles are available here: 👉 https://autotechtools.ca Start by introducing yourself: - Where you’re at in your career - What you’re studying for (or working on) - What you struggle with most in the shop Let’s build better technicians — not just pass tests. 👊