How to replace alternator on 2003 lexus es300?
John Campbell 
If your alternator fails, you will need to replace it as soon as possible. Here is a guide on how to do so on a 2003 Lexus ES300.
1. Park the car and disable the ignition.
2. Remove the negative battery cable.
3. Remove the air cleaner assembly.
4. Remove the plastic under-panel from under the hood. You can do this by removing the six nuts holding it in place and pulling it out of its clips. This will give you access to a few things, mainly where your battery is held down as well as some other items you might need to remove later on.
5. Jack up the car and put it on jack stands.
6. Remove the battery. This is done by removing the hold-down bracket as well as the 10 mm negative bolt from the battery post. Pull out your battery and set it to the side appropriately.
7. Unscrew all eight screws around your air filter housing. These are really small, so I recommend using a magnetic screwdriver so you don’t lose them. Pull off the air filter cover and remove the foam element inside.
8. Remove the three bolts holding on your air intake tubing. There is one located under where your battery was held down along with two others you will see when looking in the engine bay.
9. Disconnect the electrical connections to your alternator. There are three total, one of which is a large connector. Be sure to note where each goes so you can put them back on correctly later on. You can now remove your old alternator.
10. Replace your old alternator with the new one by reversing the steps above.
What is the use of alternator on 2003 lexus es300?
The alternator produces electricity so your car can run, and recharges your battery when you start the engine. A healthy alternator ensures that the battery is fully charged; this allows you to more efficiently use its power, and decreases wear on parts such as your starter. A faulty or failing alternator will make it hard to start your car, and can eventually leave you stranded. It’s important to replace a failing alternator as soon as possible to avoid further issues.
