Factory Service Manual - What You Need to Know

A Factory Service Manual is a service repair manual published from Original Equipment Manufacturer or OEM that tells you how to repair, diagnose, and  maintain your car or components inside of your car.

There are also aftermarket service manuals from other company such as Haynes, Bentley, and  Chilton.  The most obvious difference between Factory Service Manual than these aftermarket service manuals is the amount of material provided.  Factory Service Manual provides detailed and useful troubleshooting charts and a multitude of diagrams you will not find elsewhere.  Because these are published and designed by your car's manufacturer, they tend to be more correct than the aftermarket service manuals and they also provide other complete information such as manufacturer-intended torque specification for almost every bolt on your car.

Another difference you will notice is that the quality of the illustrations.  The illustrations in the Factory Service Manual are drawn to the proper size for the page upon which they will rest, and as such they tend to have uniform line weights through out the manual.  Illustrations in the aftermarket manuals tend to be general enlarged or reduced and usually poor quality, especially in the case of detailed diagrams.  Aftermarket service manuals also usually try to cover range of years of your vehicle model, which means that if your car is a 1999 Toyota Corolla, the aftermarket manual will try to cover from 1996 to 1999 in the same book.  Even though 1996 to 1999 Corollas look much the same, there are still some significant differences on the inside.  On the other hand, Factory Service Manual is year specific, and you will get the manual for your year model.

All that being said, this doesn't mean aftermarket service manual is not worth getting.  They can still provide you general information.  If you are going to do anything more than just casual maintenance on your vehicle, you should have the Factory Service Manual and not an aftermarket one.  It is easier to use, covers more detailed information, and they can come in two forms: book or CD depends on your manufacture. One thing I like about CD Factory Service Manual is that they have quick link which allows you to jump to the other referenced section in instant second.  In the book form, you would have to keep flipping pages.  It's all based on your preference.