Car died one day. Battery was flat. After recharging i got my car running again. Voltage was very low - 12,1-12,8v . So i decided to replace alternator. Some how i got my screwdriver falling between alternator and car body so a bit sparks flew and blew the ALT fuse.
Anyway. Replaced that and replaced alternator. Everything seems OK but red battery light wont go off. It will if i shut down the car. No fault codes, all fuses in fuse boxes are fine. Voltage 13,9-14 when cold and 13,6 when engine is fully warm. 4wire socket to alternator was a bit oily. Previous owner probably spilled some oil and it has been flowing down the wire.
Found some post that someone had same issue and had blown his 7,5A ALT-S fuse but my car doesn’t have it. There is a place for it but it has only power supply pin.
checked neg and positive wires, all good. Replaced one engine-to-body cable, cleaned battery terminals and what not.

any ideas what to do? I can’t figure it out and it’s driving me crazy. Am i missing something?

 

The alternator you used to replace the old one, was it an oem or denso? Or some other brand?

 

new one is some other brand. Can’t remember what name was.
It shouldnt matter so much ‘coz voltages are good. Ecu power is same as voltage on battery and alternator. So ecu gets the power it needs.
only thing that i can think of is the 4wire socket. Maybe there are some poor connections

 

Your new alternator could pump regular voltage, but what about driving voltage did you check that? It's possible it cuts out voltage and that your new alternator is not providing power in the higher revs. Happens all the time when you buy cheaper off brand stuff. I would rather see you rebuild your old alternator with oem parts rather then.

Also have you tried swapping in a new battery, see if you have another battery off someone that you can swap into your car. Does the car crank the starter just fine or does it lag a bit? What is the battery voltage with the car turned off and after being parked for awhile?

 

Drove around for an hour and voltage was all the time 13,5-13,6v. Even with rear defroster on, full beams and music blasting it was still 13,5.
everything seems to work just fine part from battery light.
battery is 2 years old. I have not checked battery voltage before starting car. And since the car starts fine i havent thought that battery could cause this.

 

Try testing the main positive electrical post on the alternator and place ground on the engine block, with the car running and see if that exposes maybe a weak ground somewhere. Kinda difficult to be honest its probably best to take it to a mechanic

 

Had full diagnostics done. No errors found. Mechanic told that the light is on because alternator pumps out 13,6-13,8v not 14,2-14,4v. But it is total bullcr*p imo because old alternator gave only 12,5v and even then no battery light was indicated.
i have to go through gs wiring diagrams and look if there is any fuse or something hidden somewhere.
it still looks like it would be logical that i have blow 7,5a alt-s fuse. But since i have early model maybe that fuse is somewhere else and not in fuse box.

 

13.8 volts at idle or while revving the engine? When you dropped the screw driver, what power terminal did it actually touch, the main power lug on the alternator itself?

 

13,8 most of time. When engine is fully warm and idle drops down to ~650rpm, then its 13,6v.
I believe it dropped on the positive wire connection right on the alternator. There is a rubber cover on it but it was a bit damaged from the top.
I found few wiring diagrams and all of them show that somewhere has to be 7,5a alt-s fuse.

 

Looks like ALT is on fuse number 14 in the engine bay fuse box, on the left side near the battery. I would grab a test light and test the tops of all the fuse boxes in the car just incase. The fuse should light up on both sides, or you can grab needle nose pliers and pull each fuse and inspect all.

Heres a diagram and fuses numbers
https://fuse-box.info/lexus/lexus-gs...007-2011-fuses

 

Time has passed and still no solution. All fuses checked numerous times.
Has anyone got wiring diagram for first production year of 3gs? Later models seem to have that 7.5A ALT-S fuse, but mine doesn´t.
At this point it actually seems that maybe the alternator´s 4-wire plug is not giving good connection or maybe some wire has some damage.

 

Take it to a shop and have them diagnose it properly.

 

do you still have your old alternator? id swap out the new alternator with a different one and see if the light goes off.

 

Thats a good idea, and maybe add new oem brushes to the old alternator

 

Sounds like the regulator got messed up when you dropped the screwdriver and caused sparks on the new alternator. That’s just bad luck and you may have to buy a new alternator. This time make sure to leave the battery disconnected until you’re completely finished.