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Hi all,
I have been fighting this for over a month now so I hope you can help. I have a 99 Lexus GS400. Back about 2 months ago the front bearing in the alternator started making noise. Also it wasn’t keeping the battery charged all the way. It was like the voltage output was not enough. Since I have not had good luck with store branded rebuilt alternators on Toyota/Lexus before I took the alternator to a local shop to have rebuilt. They confirmed it had a bad bearing and brushes. I got the alternator back and replaced the battery at the same time. Once I put the alternator back on the car it would not charge. I took the alternator off and took to the local Oreilly to have tested. It tested good and was making 15v. So I was stumped. Long story short here is what I have tried:
Ran brand new ofc 4 gauge wire from the battery negative to the bottom mount bolt of the alternator, from the battery negative to the firewall/body ground point, and from the battery positive to the alternator output stud
Double checked proper voltage on the 3-pin alternator connector (Field, sense, and dummy light)
Ran a wire from the 3-pin alternator center “field” pin straight to the battery positive as this is the only thing it needs to “turn on” and charge (confirmed on test bench as center pin on 3 pin connector)
Sanded and cleaned every ground and positive point where I ran wire
Ran the engine up to 2k rpm just to see if it was not working at idle
Voltage drop and resistance tests on all ground wires andSo as you can see I have pretty much duplicated the test bench scenario on the car by running all new wire bypassing all stock wiring and energizing the field pin on the voltage regulator directly. A friend of mine is a master toyota tech and even he is stumped. If I pull the alternator off the car and take to get bench tested it works and passes all tests but on the car it refuses to work. Before I go out and spend a couple hundred dollars I don’t have right now on a new denso alternator is there anything yall can think of that I may can try to make this one work on the car?
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If there is no output sounds like your alternator is dead. I take it the battery light is on?
If you do need an alternator Get a factory Toyota one. Otherwise you will be right back
where you started.https://www.ericthecarguy.com/faq/solving-automotive-electrical-problems?start=2#ChecktheBattery
Make sure you have 12V on heavy Bat wire with the engine off. With the vehicle running there is a white blue wire on terminal G1 should have battery voltage. If not check Alt s fuse 5A. The red blue wire is for your bulb in the dash and I think the pink blue wire is a computer monitor circuit. If all this test good the alternator is most likely bad. Also check and make sure your battery connections are clean and tight. I would install a new alternator. not a rebuilt unit.
[quote=”ArmedsouthernEr” post=173325]Make sure you have 12V on heavy Bat wire with the engine off. With the vehicle running there is a white blue wire on terminal G1 should have battery voltage. If not check Alt s fuse 5A. The red blue wire is for your bulb in the dash and I think the pink blue wire is a computer monitor circuit. If all this test good the alternator is most likely bad. Also check and make sure your battery connections are clean and tight. I would install a new alternator. not a rebuilt unit.[/quote]
With the engine off I get 12.7v after fully charging it with a battery charger and letting it sit for an hour. With it running I get about 11.8-12v. The alt-s wire does have voltage. I forgot to mention I did check all fuses also. I just have been fighting this for over a month and am tired of dealing with it. A denso (OEM for this car) rebuilt alternator from Denso runs around $190. I just did not want to spend that if there was something you guys/gals could think of that I could try to get it to work. It just baffles me how the alternator tests good and works on the test bench but not on the car.
1. What is voltage at battery cables with car running?
2. How many times has current alternator been bench tested?1. 11.8v to 12.1v
2. 5 times. 3 at oreilly 2 at the place that rebuilt it. each teat was ran at least 3 times each.1. It tests good bench testing but not over 12V when using voltmeter at battery cables with car running?
2. I have seen this before caused by a ground issue and just went through a ground issue on a porsche that took me 3 times of changing connectors to resolve.
3. I seen you have tried very hard to isolate the ground wire from being the cause but that still could be the cause.
[quote=”BubbaGarage” post=173351]1. It tests good bench testing but not over 12V when using voltmeter at battery cables with car running?
2. I have seen this before caused by a ground issue and just went through a ground issue on a porsche that took me 3 times of changing connectors to resolve.
3. I seen you have tried very hard to isolate the ground wire from being the cause but that still could be the cause.[/quote]
Yes on 1. That is what baffles me. Maybe I can remove the stock ground cable and only rely on the 4 gauge new wire. The engine ground IS the bottom alternator bolt and the starter doesn’t have an issue so I at least know the ground is good.
After thinking more about this maybe it is something within the alternator not grounding right. When being bench tested the ground goes on a bolt on the rear cover and not the bolt hole on the case. Maybe if I run a short ground wire from the bottom alternator bolt to one or more bolts on the rear cover that may help. At least it may be worth trying before I buy a new alternator.
I agree 100% on temp ground wires……..add a few of them. Ground issue has to be problem unless bench test is a bad machine. Maybe ask alternator rebuild place if they will loan you a alternator? I have had junkyards that will do this sometimes and I offer them $20 for the trouble.
perform voltage drop test on the ground wire however I would point out that the alternator and the starter both use the engine block for a ground.
[quote=”BubbaGarage” post=173360]I agree 100% on temp ground wires……..add a few of them. Ground issue has to be problem unless bench test is a bad machine. Maybe ask alternator rebuild place if they will loan you a alternator? I have had junkyards that will do this sometimes and I offer them $20 for the trouble.[/quote]
We were on the right track here. I got the alternator off the car and was looking at adding the grounds to the rear of the case when I decided to pull the rear cover off. This is what I found:
Immediately I noticed a missing screw/bolt around the circled area. So I pulled the alternator off an old engine I have in the shop (same 1uzfe, just non-VVTi but alternators are similar enough). Here is what it looked like:
So I took the screw out and put in the rebuilt one. The blue cover also was not on mine but that doesn’t keep it from working so I just left it alone. I went ahead and added the 2 grounds to bolts on the back of the case and ran it around to the bottom mount of the alternator when I installed it back on the car. Fired it up and got this:
FINALLY it is charging. Thank you guys for jogging my thought process enough to check this. Now I don’t know if it was that screw that fixed it or the new grounds. I can disconnect the grounds easily enough and see if it still works. If so I will remove the back case grounds and roll with it. I am sooooooo happy right now!
Seeing as you replaced that screw and now it charges I bet that’s the fix. Ground problem doesn’t seem possible as all the redundant grounds you added and the fact that the starter uses the block as a ground as well and you were having no other issues other than the alternator not charging. Most times on a bad block ground you will have multiple other electrical issues associated with it. This is exactly why I prefer to install new alternators. If we have a problem our commercial parts guy will take care of it, as well as the customer gets a warranty. Glad you figured it out.
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