My niece has a 2001 IS 300 which has been having issues with the battery/alternator. I went to the car yesterday and it was DEAD. So I pulled the battery, took it to AutoZone, they charged it and said the battery is good. So I clean the battery post and the cable connectors, install the battery and fire it up. I have a www.ScanGauge.com (an OBD2 tool) so I plug that in and watch the volts.
When started the volts read 14.1. I take the car for a drive and the first stop or 2 the volts drop to 13.6 - 13.8, no big deal. About a mile away, 3 minutes into the drive, I stop at a light and the volts drop to 12.3 - 12.4. I drive a few miles and at stops the volts drop as low as 11.7. I figure the alternator is dropping off line and at low idles, I may just be reading battery voltage. It goes a little higher when I turn off the AC and head lights.
So I figure the alternator has an issue. I tell my brother and suggest a Toyota or Lexus part, he calls his son that works at a Lexus dealer, they call me back and tell me to go to a local auto parts store and get a new alternator for $125 with a lifetime warranty. I don't put up a fight and go forward and install the store box alternator.
I crank the car, 14.4 volts, I drive the car and a mile down the road I stop at a traffic light and the darn volts drop to 12.2 - 12.4. Another mile down the road and it drops to 11.9 volts. While driving it is between 13.8 - 14.2 volts.
Did I get a bad alternator from the store or does this car have another issue?
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This to me seems absolutely normal. My bike does the same thing as well as most of the cars I have purchased/ Tested.
Generally speaking at idle it is just making enough power to keep the car on, you have to really hit over 2k-3k to start making power. Generally i would see around 14 around 2500-3000rpms and it would level around either around there or 15 depending on the car.
I will keep an eye on it. Every other car I hook my ScanGauge up to reads 13.4+ volts at idle. This one reads 14.2+ when I initially start the car. It doesn't start dropping down until the car gets warmed up.
Does the battery light on the gauge cluster ever come on? I would say that is not normal and would try another alternator. I have seen a few cars come into my dealership with issues very similar to this. I always recommend an OEM one have never had one come back. I see this mostly on ES and GX, but that could happen on any car really.
- ASE Master/Lexus Master Certified Technician -
Autozone and Oriella changed manufacture on reman alternator with bad regulators. I changed my alternator on my dads minivan 4 times in one year before going back to OEM.
What you are posting is somewhat normal if the battery is near fully charge and at idle for the most part. If thats the voltage while driving 11.7 is ok but normally it will be low 12s for me and on very warm days it dips into high 11s for a few seconds then jumps back up when the fans kick on.
Thanks OnePointOn, I recommended a OEM alternator but hey.
DatSRBoi: The only time I have ever seen under 12v on my ScanGauge was right before a alternator or regulator change.
I'm going to recommend they change it again this week under warranty and see what happens. It starts out over 14v and while driving it is over 13.4, it drops under 12v when the car is warmed up and at stop lights.
I would recommend taking the batt. to charge again. It's always best to have a fully charged batt. when installing a new alternator. I've gone the auto parts store route before and because they are rebuilt (the one I bought was) you don't really know what you're getting yourself into. Long story short... I had to buy a OEM Denso Alternator from the dealer which was rebuilt as well but it worked out flawless! Good luck!
You can start the car and then disconnect the battery and take voltage. Technically the car should stay running as the battery is only needed to crank the car. You can take your voltage then eliminating the battery. If the car dies, there's your answer.