Hi,

I'm on Alternator #5 in as maybe 7 months.
Two professional mechanics have looked at the car.
They seem to be very good at their jobs with lots of experience and good online reviews.
Neither has diagnosed anything specific enough to fix.

The issue seems to be most noticeable when idling with the A/C and lights on.
Over a month or two, in Florida heat, this scenario eventually leads to a low voltage situation.
The issue is erratic but progressively worse.
It's usually 13.7v+ when the car first starts.
Then it drops as the days progresses.
In the early stages it drops to 12.5,6,7v.
Later it's down below 12, and lower just below it fails.

My mechanic says that at idle the two things are wrong.
1) The computer should increase the idle when the a/c is on and this is not happening.
2) When the issue occurs there is little charging at idle.
Early in the cycle the charging is fine when driving.
Later in the cycle not so much.

I talked to a Lexus mechanic today.
He seemed to think I was crazy and was non-committal about finding a solution or quoting for a diagnosis.

Nobody seems to be able to help other than changing alternators every month or two.
I am thinking about upgrading to a high output alternator but that might be a large waste of money.
Any other suggestions would be very welcome.

 

What year is the car and do you know if the alternator is the new style which is controlled by the ECM. If so there is a module that feeds back to the ECM telling it when to charge. Also how new are your batteries and have you had them load tested to see what percentage of charge they are at. Look up electronic alternators and how they function. How are the replacement alternators tested prior to installation. Also what are your driving habits . Do you take short runs or is it highway speeds. I am not familiar with the ES300 system but the ES350 alternators usually put out 14.2 volts at idle .

 

Interesting read http://carspecmn.com/toyota-and-lexu...tor-diagnosis/

 

The car is a 1997 es300.
The most voltage I ever see is like 13.9 when the car first starts. It drops after maybe 10 minutes.
We drive both long and short trips. The power deficit is very visible at idle.
The battery is pretty new, March-2016, when the 1st alternator failed. Its tested every failure.
I'll research the ecm / alternator connection.

Thanks for your help

 

Do you live inland or by the ocean?

Either way, humidity and salty air can really corrode your cables. If the battery and alternator are both new, and the PCM/ECM is fine (usually is), then it's fairly likely that you have a problem with the cables.

Eventually cables in humid environments corrode. I wouldn't expect to see cable corrosion in Phoenix but anywhere with humidity and precipitation...

 

We live at the beach in Florida.\It's hotm humod and the a/c is always blasting.
I'm 100% sure the issue is somewhere in that previous sentence.
That said, all the cables have been inspected, cleaned and reinstalled.

Thanks for your input.

 

It sounds like you are referring to the cable ends but I'm talking about INSIDE the cables. I've pulled some clean looking cables off of cars having charging/electrical issues...slice them open and they are all fat and green and corroded on the inside. I can't explain how it happens but it does. Your terminals and connections could look mint and the cable looks fine from the outside but it is simply internally compromised.

If you live in salty air and the cable are original, I strongly suggest replacing them, or at least dissecting a 3-4" long section so see how they look inside. You can always tape them up and keep going if they are fine.

 

Thats good advice and an easy job.
Thanks.

 

You might see it on the main cable from the battery to the alternator but it seems to more often affect the large ground cable from the starter to the chassis that usually resides under the car.