The serpentine belt on a Lexus RX 300 allows the front engine accessories to turn in harmony, keeping them all in line. The belt is made of rubber, and over time it can stretch out a bit, eventually failing. When this happens, all of the engine accessories stop working and the Lexus won't run properly. Fixing the problem means replacing the serpentine belt with a new one, which can be done in about an hour with the right tools.
Lift up the front of the RX 300 using the jack and put it down on a pair of jack stands located just behind the front wheels. Take off the passenger side front wheel using the tire iron and set it to the side. Unbolt the under cover and apron seal from the engine bay using the 3/8-inch ratchet and socket.
Loosen the A/C compressor bolts using the 3/8-inch ratchet and socket. Pull the A/C compressor toward the middle of the engine and pull the belt off of the A/C compressor pulley. Take a note of the proper running of the belt, then remove the belt entirely from the engine.
Set the replacement belt onto the engine using your hands. Make sure that the belt is run the same way as the original. Pull the A/C compressor away from the engine and tighten down the A/C compressor bolts using the 3/8-inch ratchet and socket.
Reinstall the under cover and engine seal to the bottom of the engine using the ratchet, mount the wheel on the hub using the tire iron and lower the SUV off of the jack stands using the jack.
