A Toyota master diagnostic technician explains Toyota fuel trims both short term and long term. Also does a demonstration of real world engine live data reading techniques.

In this video I continue my series on how Toyota engine controls work. In this part of the series I will cover Short term fuel trims and Long term fuel trims.

First I'll cover the basics of fuel trims, Then I will cover the common diagnosis uses and the common misconceptions about fuel trim. Slightly elevated or decreased fuel trim is not a problem!

Many people assume that a perfect zero fuel trim is what's needed and that is not the case, I've seen many people spend a lot of money in the pursuit of dropping their fuel trim down to zero without success and with big disappointment I hope this video helps clarify that!

Also for majority of this video I will explain a very simple and basic data list to show how things work in a diagnosis situation. I want my viewers to slowly start seeing that car diagnosis is not just experience and mechanical know how. It's actually involves a lot of simple science and actually a specific form of Art!

Understanding how things work is the stepping stone on understanding how to approach diagnosis and repair. I see a generation of parts replacement technician without attempting or wanting to understand how everything works. I hope this series helps someone out there truly start to understand how diagnosis is carried out from a live data list.


I simulate some common issues like a vacuum leak and a bad coil so you can see how the computer reacts to these situations. Also I share some basic tricks that you won't read in a book or a repair manual on injector diagnosis! More to come from this series!

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0:00 Intro
0:52 Fuel Trims
4:41 Fuel Trim Diagnosis
11:28 Live Data Demo and Tips