Like most front wheel drive cars the Toyota Matrix has a serpentine belt that drives the alternator, water pump, air conditioner , and power steering pump. Our 2003 Toyota matrix got to where it had 50,000 miles on it and the old belt started to give symptoms of being stretched because the automatic tensioner was no longer able to put adequate tension on the belt to keep it from slipping when the air conditioner was turned on.
The first "heads up" advice I need to mention is that the book in the auto parts store called for three different belts for the Matrix and the book wasn't clear as to why there were three possibilities so I bought all three with the understanding that I would bring back the belts I didn't need. It was a good thing that I bought all three because the one that I was going to get was too short and I would have had to return to the auto parts store any way, so if you can take the old belt in first you can save yourself a trip back to the auto parts store.
To replace the old belt the first thing that I did was draw a diagram of the pulleys showing how the belt either went over it or under it, and where it went next. I recommend doing that unless you have a shop manual, which I don't..yet. Once you have your diagram drawn you will need to remove the old belt by taking a wrench, that I think is a 15mm and put it on the bolt in the center of the spring loaded tensioner pulley and move the pulley in the opposite direction of the belt to relax the tension on the belt so you can remove it. You need to be somewhat of a contortionist to do this, but it isn't that difficult as long as you have a good grip on the pulley.
Once the old belt has been removed, using your diagram, install the new belt up to the tensioner so the tensioner is the last pulley the new belt needs to go over. Then using your wrench, relax the tension on the tensioner once again and slide the new belt into place and allow the tensioner to contact the new belt and remove your wrench from the pulley. Double check the belt and make sure that it is fully engaging all of the pulleys before you start the car. People sometimes make the mistake in thinking that a serpentine belt will locate itself on the pulleys once the engine starts and in rare instances that works that way, but a serpentine belt is not like a V-belt with the locating characteristics of a V-belt, but they usually stay in place if they are installed with full contact on all of the pulleys.
