Hi
07 RX 350, car won't start after hazard lights were on for 20 mins, jump start it went to auto zone they said battery is bad, after recharging it they said everything is working fine, they did 2nd test and said alternator is bad, Advanced auto parts test shows everything is working fine, I don't know what is bad.
When car is running I get 13.4 volts, with load get 13.2 volts that really low or is it normal for RX can any one tell me what do you get?
In the morning I see battery is 12.4 volts and alternator shows 14.02 volts but with in 2 mins it goes to 13.2 volts.

 

The last time I checked I believe the voltage was at 14V + when the vehicle was running, most likely a diode failing in the alternator.
Google " verify alternator diodes", which can be verified with a multimeter.
That would be my guess assuming the battery tested fine & there is no parasitic draw somewhere in the electronic system.

 

Do you drive it everyday? If you don't, if you can let it sit a week. test it after a week, and see how much it dropped. If it drops a lot your battery is on it's way out. If you don't want to buy a new battery right away, you can leave it on a trickle charger when you aren't driving it. I do this weekly for my motorcycles (fair weathered rider).

Sounds like your alternator is on it's way out. My understanding and personal experience (I run a live monitor on the volts to the battery on an older car). Usually the alternator charges at 14.2 with the engine running, when the battery is fully charged, it drops to as low as 13.5.

 

In the morning I see battery is 12.4 volts and alternator shows 14.02 volts but with in 2 mins it goes to 13.2 volts.

 

The odds are better than average a diode is failing in the alternator.
The best bet would be to purchase a reconditioned alternator at a parts store, although you would need to hand in your old alternator as an exchange.
Changed many alternators with that method, once done, the alternator lasted for as long as I owned the vehicle.
A new alternator is in the $300. range, reconditioned is in the $150. range depending if your alternator is 100 amps or 130 amps.

 

^ have a 996. rebuilt porsche alternator is $600. so to me $300 ain't bad at all.

 

From Toyota experience, stay away from Big Box Remanufactured alternators. Stick to OEM Denso new or built which can be had at your Toyota/Lexus dealer or Rock Auto.

If you have them, try rebuilder shops and have them refresh your current alternator (don't swap). Most of the time, you just need new brushes, bearings, and possible the diode which doesn't cost much. Around me a rebuild runs about $100 and I keep my OEM alternator.

 

I actually Put OEM alternator last august and still under warranty but if it is not the alternator causing problems than I have to pay $150 dollars for diagnosis to the dealership that's why I'm trying to make sure it is the alternator or the battery?

 

This lil baby will help you diagnose the issue. I have the wired version. no affliation.

http://www.ultra-gauge.com/ultragauge/

You can run it in real time, all the time. I have one in my other car, and that is how I caught the alternator dying. it wouldn't charge when in gear (battery would be 12.2v), but at idle, neutral it would charge at 14.2 . eventually it stopped charging totally.

I will say, the ultragauge has specific hook up parameters to work with the RX. It isn't plug n play and forget about it.

 

If you access to techstream, that can measure voltage too. I use it all the time alongside my multimeter.

 

Thanks
What makes the voltage go down from 14 to 13.2 with in couple of minutes?

 

Perhaps since the alternator is under warranty, whoever installed it should verify it at no charge & replace it if defective for starters, then if issues persist, focus on the battery.
If you battery is over 5 years old, it would be time to replace it.

 

A few things that come to mind is a failing diode, uneven contact with the brushes, or something pulling heavy amperage or dropping the voltage like a subwoofer amp. I doubt you have an aftermarket setup but my subwoofer setup on my camry can drop the voltage from 14.2 to 12.9 on full tilt.

 

I don't know the cause, but I have replaced 2 alternators with the same symptoms on two different RX's.

While you have a voltmeter on the battery, try turning things on that use juice: headlights, bun warmers, climate control fan on high. If the alternator is failing, the voltage will drop when you turn those things on. Mine dropped to 12.3 volts with everything on. If the alternator is good, the voltage will stay at 14V or above even with everything on, at idle.

 

It stays at 13.3 v
where is the red wire connects at alternator that coming from the battery? I would like test voltage at alternator end?
thanks