DIY:CHARGING SYSTEM FULL DIAGNOSTIC(alternator/battery) - Page 5 - Lexus IS Forum
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post #61 of 71 (permalink) Old 09-27-2017, 01:39 PM
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Alternator issue?

I replaced the alternator on my '99 ES300 as its output was 17.6V. I decided that I should get the battery checked out in case it was damaged (the case puffed out a bit due it being overcharged). The battery failed when they loaded it down to 8-9V. Got another battery as a loaner, and the mechanic noticed the alternator was hot - too hot to touch. He thought I may have a bad alternator, it was getting hot due to putting out too much current. I took the car into the starter/alternator rebuild shop and the alternator tested good in the car with the automated tester, but was putting out 60Amps at idle. The shop owner said it should be more like 20 and I had a short somewhere but the alternator was ok. He said I could remove the alternator and bring it back for a bench test to rule out the alternator for sure.
I should state the the voltage at idle and with all accessories on is good. 12.4 at idle, and 14.4 with accessories on.
I called my mechanic and told him what was going on. He said that he did not think that 60 amps at idle was excessive. His comment about the alternator being super hot was that all parts under the hood are going to be hot after driving for some time......
Too many opinions. But I'm here for yours Please help.
Thanks
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post #62 of 71 (permalink) Old 09-27-2017, 04:30 PM Thread Starter
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Originally Posted by kevstang67 View Post
I replaced the alternator on my '99 ES300 as its output was 17.6V. I decided that I should get the battery checked out in case it was damaged (the case puffed out a bit due it being overcharged). The battery failed when they loaded it down to 8-9V. Got another battery as a loaner, and the mechanic noticed the alternator was hot - too hot to touch. He thought I may have a bad alternator, it was getting hot due to putting out too much current. I took the car into the starter/alternator rebuild shop and the alternator tested good in the car with the automated tester, but was putting out 60Amps at idle. The shop owner said it should be more like 20 and I had a short somewhere but the alternator was ok. He said I could remove the alternator and bring it back for a bench test to rule out the alternator for sure.
I should state the the voltage at idle and with all accessories on is good. 12.4 at idle, and 14.4 with accessories on.
I called my mechanic and told him what was going on. He said that he did not think that 60 amps at idle was excessive. His comment about the alternator being super hot was that all parts under the hood are going to be hot after driving for some time......
Too many opinions. But I'm here for yours Please help.
Thanks
What do you mean by automated tester when he checked the alt's amp output? A clamp on DC amp meter? He load tested the whole charging system? The battery is in parallel with the alt, so I hope he did not disconnect the battery while the car is running (you can kill an alt instantly as well as cause other damage).

I see a number of things that don't sound right. No way will an alt put out 60A at idle, even if you had every accessory on and a 2kW stereo system blasting. 20A still sounds high depending on the state of the battery and what accessories are on. Another thing, 12.4vdc at idle is no good and it is not charging the battery. It should be between 13.2-14.8vdc at idle and not drop below 13.2vdc even with the engine at operating temperature and some accessories on.

What does the voltage read at the battery with the car off? It's possible you have a drain somewhere but I would likely pull the alt and have it bench tested, it's the only absolute way to be sure of what it can output based on rpms. It is always a good idea to bench test any alt that is suspected bad, even before you replace it.

'02 IS300 MSM LSD
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post #63 of 71 (permalink) Old 09-27-2017, 11:55 PM
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Originally Posted by jasonm4 View Post
What do you mean by automated tester when he checked the alt's amp output? A clamp on DC amp meter? He load tested the whole charging system? The battery is in parallel with the alt, so I hope he did not disconnect the battery while the car is running (you can kill an alt instantly as well as cause other damage).

I see a number of things that don't sound right. No way will an alt put out 60A at idle, even if you had every accessory on and a 2kW stereo system blasting. 20A still sounds high depending on the state of the battery and what accessories are on. Another thing, 12.4vdc at idle is no good and it is not charging the battery. It should be between 13.2-14.8vdc at idle and not drop below 13.2vdc even with the engine at operating temperature and some accessories on.

What does the voltage read at the battery with the car off? It's possible you have a drain somewhere but I would likely pull the alt and have it bench tested, it's the only absolute way to be sure of what it can output based on rpms. It is always a good idea to bench test any alt that is suspected bad, even before you replace it.
Thanks for the reply. By automated tester, I meant that it stated the alternator was good based on attaching the leads to the alternator output stud, and to ground. A clamp on DC ammeter was used. The battery was not disconnected.

I may have misstated the output voltages. I just double checked with the following readings noted:
Voltage at battery with the car off: 12.63V
Voltage at battery with the car on and no accessories except driving lights on (it was dark outside): 14.4
Voltage at battery with the car on and accessories on at idle (headlights, A/C on, fan on high, radio): 14.34
Voltage at battery with the car on and accessories on at 2K RPM (headlights, A/C on, fan on high, radio): 14.4

I only had the car on for a couple of minutes max to record the voltages. After I turned the car off, I touched the alternator and it was very hot. The exhaust manifold was very warm too, but I would think the alternator would not heat up to the same temp as the engine until the car had been running longer.

I will take the alternator off and take it to Autozone where I bought the rebuilt unit.
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post #64 of 71 (permalink) Old 09-28-2017, 04:19 AM Thread Starter
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Thanks for the reply. By automated tester, I meant that it stated the alternator was good based on attaching the leads to the alternator output stud, and to ground. A clamp on DC ammeter was used. The battery was not disconnected.

I may have misstated the output voltages. I just double checked with the following readings noted:
Voltage at battery with the car off: 12.63V
Voltage at battery with the car on and no accessories except driving lights on (it was dark outside): 14.4
Voltage at battery with the car on and accessories on at idle (headlights, A/C on, fan on high, radio): 14.34
Voltage at battery with the car on and accessories on at 2K RPM (headlights, A/C on, fan on high, radio): 14.4

I only had the car on for a couple of minutes max to record the voltages. After I turned the car off, I touched the alternator and it was very hot. The exhaust manifold was very warm too, but I would think the alternator would not heat up to the same temp as the engine until the car had been running longer.

I will take the alternator off and take it to Autozone where I bought the rebuilt unit.
Well I can tell you that all the numbers above look great. I probably wouldn't pull the alt at this point based on the new data. If it's still pulling 20A then the problem may be elsewhere, but 20A really isn't too high depending on what was running. The alt will get hot quickly with the manifold right below.

'02 IS300 MSM LSD
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post #65 of 71 (permalink) Old 09-28-2017, 07:38 AM
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Originally Posted by jasonm4 View Post
Well I can tell you that all the numbers above look great. I probably wouldn't pull the alt at this point based on the new data. If it's still pulling 20A then the problem may be elsewhere, but 20A really isn't too high depending on what was running. The alt will get hot quickly with the manifold right below.
From my initial post, the current draw as measured at the starter/alternator shop with the alternator installed in the car was 60A. I planned to pull it this morning, but maybe I will wait. A buddy is bringing his clamp on ammeter over later today.
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post #66 of 71 (permalink) Old 10-04-2017, 12:06 AM
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Thank you for this tutorial!! I just bought a 2001IS300. Ive never owned Toyota before. Always been a Honda guy but I got a great deal on this car. Bought it a week ago. The end of sept 2017. One owner 115k on the odo. Did a car fax. Nothing popped up. So no major issues. Always serviced at the dealership.
Today, the car started acting funny. Gauges go in and out. Loss of power to the engine. All the signs of an alternator issue. The battery was brand new when I got the car.
Then I read another post. Could be the drive belt being loose. Makes sense. It?s too late now, but I?m gonna get it checked tomorrow and see what?s up. Have the charging system checked and if that?s all good then it more than likely is the belt. If not that, then a few other likely suspects.
Like I said, I?ve always known Honda and can fix most issues but I?m in a whole new world with Toyota. The basics are all the same of course. Just the nitty grittys.
Thanks for the tutorial again!!!!
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post #67 of 71 (permalink) Old 11-27-2017, 07:22 PM
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My battery is 3-4 years old and my car can not be fired. The AAA tech came to replace the battery and he told me he could not do the battery analysis and he detected excessive ripple(660mV). He told me if I replace the battery now without fix the voltage regulator problem he can not issue me the 6 year warranty of the battery. I then went to Autozone and the person told me the battery is bad and I need to replace the battery first before he can do any diagnose for the charging system. Those two person gave me two different options, which one I should follow? Is the ripple test reliable under a dead battery? Any input is appreciated!
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post #68 of 71 (permalink) Old 11-28-2017, 05:15 AM
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There needs to be a good battery to get a correct reading.
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post #69 of 71 (permalink) Old 11-28-2017, 08:15 AM
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Thanks for your input and sorry for the double post!!!
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post #70 of 71 (permalink) Old 09-20-2018, 04:23 AM
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Jason,

I am confused with my battery. It starts fine but with the key in "On" but engine off, my voltage is 11.6v. While driving, its 13.7v. I tested this at the battery posts. I also have a usb digital volt meter and they match.

Isnt the battery dead below 12.3v. The battery is only 9 months old. Do I have a dead cell in the battery?

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post #71 of 71 (permalink) Old 09-21-2018, 11:11 AM
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Jason,

I am confused with my battery. It starts fine but with the key in "On" but engine off, my voltage is 11.6v. While driving, its 13.7v. I tested this at the battery posts. I also have a usb digital volt meter and they match.

Isnt the battery dead below 12.3v. The battery is only 9 months old. Do I have a dead cell in the battery?
It is fine. But on the worn side. For peace of mind. Just go by an auto parts store and get it and the alternator load tested.
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