Does anyone have an idea on my problem?

I have a 2009 IS250

When I put my "pedal to the metal" my battery light comes on at around 3k-4k rpm, it caused me to loose all power on the motorway (was a bit scary as lost all PAS, and hazards didn't work either) at first I thought faulty alternator so with that I replaced it along with a new battery. The issue stopped for a couple of months and it has now started to happen again.

Does anyone know if there is another solution to my problem, maybe something else that could be causing this power drain???

 

Remove the alternator, return it and put $$$ on top & buy a higher quality alt.

 

I got the alternator from main dealer, its a factory fitted one. I even asked the dealer if they had any ideas and they were scratching their heads.

 

As said above, a good battery, and nothing less than a Denso alternator. These cars are really picky!

 

​​​​​​Hmm......have you inspected the serpentine belt and the belt tensioner?

The grooves of the belt should look "matte black" in color, NOT glossy black. If the grooves are glossy, the belt is slipping and needs to be replaced.

If the belt is slipping.......WHY, is it slipping? Is it just old? Or does the problem arise from a failed belt tensioner?

Regarding the belt tensioner, they don't last forever. Usually when they fail, it's the bearing that fails. You'll know when the bearing fails because you'll hear it squealing.

However, sometimes the spring rod in the tensioner body becomes weak. When this happens, the little indicator mark on the tensioner arm will shift out of alignment with the hash marks on the tensioner body/bracket........Inspect the indicator and hash marks for proper alignment. If the indicator mark is not between the hash marks, replace the tensioner.

One way to check for a loose belt is to turn on as many electronic stuff in the car: High beam lights, windshield wipers, radio, air conditioner, etc..... Turn everything on. Drive the car and note when the battery light turns on. Next, turn every off and do the same thing, note when the battery light turns on. If you reach higher RPM with everything off, this is a good indication that the belt is slipping for one reason or another.

You can freely spin the alternator pulley with your hand, but when it's on the engine spinning fast, it makes resistance as it produces energy. The more energy it produces, the harder it is for the engine to spin it.

Good luck.