Obtain the necessary tools. You will need a ratchet or wrench, a breaker bar, and a tensioner tool.
Locate the serpentine belt. It is usually located at the front of the engine and connects various components such as the alternator, power steering pump, and air conditioning compressor.
Loosen the belt tensioner. Use the tensioner tool to loosen the tension on the serpentine belt. This will allow you to remove the belt from the pulleys.
Remove the belt. Once the tension is relieved, you can remove the serpentine belt by sliding it off the pulleys.
Inspect the belt. Check the serpentine belt for any signs of wear, cracks, or damage. If the belt is damaged, replace it with a new one.
Install the new belt (if needed). If you are installing a new belt, start by placing it around the crankshaft pulley. Then, work your way around the other pulleys, making sure the belt is properly seated in each one.
Retighten the belt tensioner. Once the belt is in place, use the tensioner tool to re-tension it. Follow the manufacturer's specifications for the correct tension.
Double check the tension. With the engine off, use your hand to attempt to twist the belt midway between two pulleys
Start the engine and check for any unusual noises or vibrations. If everything seems normal, you have successfully tightened the serpentine belt on your 2003 Toyota Sienna.
