Possibly the alternator bearings are going out, the belt might be adjusted too tightly, or another device powered by that belt could be going bad. The water pump is commonly powered by the same belt as the alternator, and the bearings in the water pump could be intermittantly siezing up momentarily. Check all pulleys used by the alternator belt, except the crankshaft pulley, to make sure that they turn freely, have no play, and do not grind when turned. When installed, the belt should have about 1/2 inch (12mm) free play along the longest reach of the belt. If there is not sufficient play, the belt will break very quickly, and all components driven by the belt will be damaged.
It could be dirty fuel injectors.
A failing alternator.
This is the best advise you will get. go to a Toyota dealer (Not any aftermarket parts store) and but a Toyota reman alternator. If you put an aftermarket alternator, you will have problems again. That's good advise from a former Toyota technician. Good luck.
bad or going bad alternator belt
Check bulbs or wireharness at back of bulbs.Switch handle that turns lights could be bad Toyo joe
A bad belt, a bad regulator in the alternator or bad brushes in the alternator.
Low refrigerant charge?
It usually means that the alternator isn't charging properly.
What causes the generator to burn out after replacing the alternator
Bearings can fail or a diode can burn out. Age is the enemy of an alternator.
Defective alternator or internal voltage regulator is bad.
Most likely the cause is a bad connection in that particular electrical circuit. There is a lot of time involved in trying to find exactly where that bad connection would be. Not worth fixing, in my opinion.
How to Tell If Your Car Alternator Is Bad Check related link below…
Alternator is defective and needs replacing.
It is the alternator....
The bearings on the alternator could be going bad. Remove the belt from the alternator then spin the alternator by hand to listen for grinding.
The positive cable between the alternator and the battery has an open circuit or break. There also is a set of wires that plug into the alternator that turns it on when the car is running. Wiring problems here can cause a alternator not to charge on the vehicle but works fine on a test stand. Some cars the alternator light in the dash causes the alternator to kick in when the engine is started. A burned out light in the dash causes the alternator not to charge.
poss alternator fault
the rotor in your alternator causes north and south mag. poles, and the wires in the stator pick up the cutting of the mag. flux and this causes a voltage in the stator leads.
Replace the brushes in alternator. refer to the haynes manual on how to do it.
I tires are good and balanced properly then look toward front end alignment and wheel bearings.
either the alternator or the voltage regulator are no good.may also be a bad battery
Bad bearings in the alternator. Best to just go ahead and replace it.
The main reason for this is a sliping drivebelt, very common after you pressure wash the engine and the drivebelt gets wet; also Check the tension on the drivebelt. Another reason may be a defective expansion valve.
no ans.. lot of causes regarding the problem