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Lexus charging system design configurations comply with what is common among most modern Japanese-designed cars. One odd-ball problem which can prevent alternator charging is crankshaft pulley internal separation. That pulley is a 2-piece harmonic balancer assembly. Its inner part is separated from its outer part by an elastic band. After millions of flexing movements, that elastic band's bond to either the inner or outer section fails. When that happens, the two parts don't instantly fly apart because the belt's side-to-side resistance holds them in alignment. But they do begin slipping. At first, the friction is high, so drivers have no warning symptoms about that failure. But as the surfaces slip, polishing and wearing away the elastic material, the outer section which drives the alternator belt progressively slows. That slowing process can take a week or 3 years of driving before the alternator light begins flickering, indicating marginal charging performance. At that point in this slowly degenerating process, you can pull your alternator, test it on an external alternator testing machine and see that it's still performing perfectly. But on reinstallation, you still see poor charging, perhaps dim headlights, flickering charge dash light that only goes out when you spin the engine faster than idle. Eventually, that slippage will become so bad that the car will begin stalling and won't restart without recharging. While it is not likely that your specific charging problem is caused by an internally-slipping crankshaft pulley - also called the harmonic balancer, but it is possible. A very quick check. Clean off the side surface of your harmonic balancer. Then apply a mark that spans the gap between the inner and outer section. Even blackboard chalk or finger nail polish, yellow crayon, what ever you have that can be easily seen. How about that old bottle of typing correction fluid which you don't use any more. Fast drying and highly visible. Now, start the engine, rev it up and down briefly, then turn it off. Next, recheck your new mark's alignment. If that mark's inside section still lines up with the outside section, your crank pulley is still good. But if you find that that line's parts are now out of alignment, you need to renew or replace your crankshaft pulley. Replacing that pulley only requires loosening the front belt at the alternator adjustment, and the rear belt at the power steering pump tension adjustment, then cracking that center retainer bolt loose. That bolt's threads are normal counter-clockwise to loosen. With the belts loose and the bolt out, use a puller to remove and replace the pulley. Years ago, auto parts stores sold replacement elastic goo that end users could apply and let cure to restore those elastic bonds. But engines spin faster now and while that's still technically possible, I tried it and it only lasted until a lead foot family member used the car about a week later. More than you wanted to know perhaps, but this ABSOLUTELY WILL happen to many Lexus cars using this mechanical drive system to the alternator. It may take 150,000 miles, 250K, or 350K. But that flexing link is somewhat like tires, belts, clutches, brake pads and many other parts which should not be expected to last forever. John