BaconMafia

Hi guys,

Before I get started, this is my first post so I apologize if I accidentally put this in the wrong place or make it too long or whatever.

Anyways, I have a bone stock 1998 Lexus LS400 with about 220,000 miles that I purchased roughly a year and a half ago. Recently, I had this strange charging system issue. One morning, I had a dead battery so I got it jumpstarted. Then, about 5 minutes into the drive, the gauges started flickering, radio went out and as I approached the red light, it died completely with no warning lights at all. I had my parents rescue me and on the side of the road, we jumpstarted the car and it roared back into life. However, once the cables were disconnected, it would die completely. We swapped that battery with a charged one and limped it home with no warning lights. Once home, we put a volt meter on it and it was only putting out 12.5 volts at idle and 2500 rpm and when the rpms dropped to idle, the battery light went on for a second and went off. With that, I removed the alternator and brought it into the local alternator rebuild guy where he confirmed it was the alternator and replaced the slip rings and brushes. He even put it on a test bench for me and saw it was putting out 14 volts with a load.

I reinstalled it and I turned the key to the on position without starting it to see if the battery light functioned and it never came on. I started the car and the put a volt meter to the battery and saw only 12.5 volts with it slowly decreasing. I checked all the fuses and did continuity checks and the fuses were fine and there was continuity from the alternator to the positive terminal. I also checked to see if there was power going to the alternator through that plug on the back and all three leads had battery voltage hinting that the power supply system functions. As for the battery light, I took the cluster out to see if the bulb was burned out only to find it is fine and was getting battery voltage according to the volt meter.

One thing I should note is that when I was removing the alternator, I stupidly forgot to disconnect the negative terminal and touched the wrench on the big black lead on the alternator to the chassis so that may have to so with this. Also, the battery is 6 month old and seems to function perfectly.

Do you guys know if the battery light not functioning has anything to so with the alternator not putting out? Do any of you guys have a wiring diagram of the charging system or any advice on what I should do? Any help is greatly appreciated.

Yamae

See these photos first.
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I have experienced a similar problem with you. In my case, the alternator was half dead. It was working poorly. The charge light was not turned on but the 3 digit chap digital meter showed 11.8V at the cigarette socket and 12.4V at the battery when idling.

It was caused by the bigger resistance between the brushes and the slip rings. Inner surface of the brush unit was burnt black and badly smelled as is sown the 2nd photo. The heat was caused by the existing resistance between those 2. Cleaning and polishing the surface of slip rings and a new brush unit fixed the problem. But that was only a temporary fix. I noticed that the oil was coming down little by little from upper side. I added a kind of umbrella over the alternator using a beer can for fear of the problem coming back. The oil was not from the PS pump but was from the head cover gasket. I had to replace the gasket as well as the spark plug gaskets.

I was able notice the problem before the alternator was completely dead and there was no need to replace it. But the invaded engine oil partially damaged the slip rings and the brush unit. Alternators dislike the oil since the surface of slip rings are damaged by the heat caused by the higher resistance when the oil is invaded and attached to it. I hope your alternator is not badly damaged.

This is just for your information.
oldskewel reported worn slip rings at the post #7 here.

oldskewel

iTrader: (1)

Yamae - sounds like your experience was similar to mine. I even have the same cig-lighter voltage gauge. I recently found engine oil (definitely not PSF) getting onto the alternator, and replaced the VCGs to address that. Still getting a little oil, but not from the VCGs, so I think it is from the camshaft seals. Not wanting to tear that open, I tried some ATP AT-205 in the oil, which might have done the trick.

BaconMafia - you said, "With that, I removed the alternator and brought it into the local alternator rebuild guy where he confirmed it was the alternator and replaced the slip rings and brushes." Are you sure the rebuild guy actually replaced the slip rings? If you look at that thread Yamae links to above, you'll see that I searched high and low and did not find any legit documentation, recommendation, or even the correct part for replacing the slip rings. Maybe your guy cleaned up the slip rings but did not replace them? It looks to me like a research project if I am to replace the slip rings.

BTW, on that project of mine, it is still sitting on my workbench, still on my list of to-do things, but not yet at the top. I will do it one day, just because there is nothing to lose, and it might be fun. If it works, I'll have a spare alternator.

BaconMafia

Thanks for the the replies guys.

Yamae, the problem you stated with your car sound exactly the same as what I had that left me stranded on the side of the road and it seems like it was engine oil from the VC Gasket is what cooked my alternator.

oldskewel, I suppose I do not have actual proof that the guy did replace the slip rings or brushes but I did see it work on the bench test. IIRC, the guy said he cleaned out the oil and did something with the slip rings and brushes.

I think the best bet is to take out the alternator and have it tested again but I am still confused on the battery light. It never comes on since I put the alternator back in even when the the engine rpm is 0. I turn the key to the on position and all the warning lights function except the battery light so something is up with that. Does that have anything to do with the alternator not putting out?

Yamae

The battery light is driven by the ECU getting the signal from the regulator built in the alternator. When the regulator is not working right, the ECU can't act and there may be a problem of no light. I worry that your regulator is partially dead.

oldskewel

iTrader: (1)

It would make a lot more sense if he replaced the brushes and cleaned the slip rings, so I'll guess that's what actually happened.

And yes, the battery light should come on when the alternator is installed, key is ON, and the engine is stopped. The fact that it does not suggests a problem with the alternator. Other things could cause it as well (burned out bulb; connector/wiring issue), but it could definitely be the alternator, and since you have other alternator issues ...

BaconMafia

Thanks for this info. This makes me feel a little better that the problem is in the alternator and not in the ECU or PCM.

I pulled the cluster out and checked for the bulb and power which both seemed fine. Hopefully there is nothing wrong with the cluster as I took the back panel off to try and see where the wires go and immediately noped out of there seeing how complicated it was.


I took the alternator out today and will bring it back by the alternator guy so see if the regulator and other parts of the alternator are the issue. I'll post back the results of the alternator and see if that is the issue.

Thanks again for the info.

BaconMafia

So I got my alternator tested today. It seems like it is functioning perfectly. The guy showed me the internals, how it works, what pins need power to work and showed it was putting out 14 volts. I put it back on my car and still the same issue. No battery light even when the engine is at 0 rpm and there is still no output. I tested the connecter that goes into the back of the alternator again and all three pins had power as well as the fuse so I have no idea why the alternator is not putting out and the battery light is not working.

Any of y'all have more hints?

aptoslexus

98 charging diagram
10A gauge fuse is good?

BaconMafia

Thanks for the diagram. Yes, 10A Gauge is fine and getting 12 volts.

I see there is a transistor after the charge light (if I am reading the diagram right). Where does the base of the transistor get power from in order to close the circuit? ECU?

I am beginning to wonder if the plug at the back of the alternator is faulty.

Yamae

The transistor gets the drive signal from the CPU in the same combination meter unit. The CPU there gets the drive signal from the ECU as a multiplexed bus signal called BEAN. The ECU is monitoring the alternator's condition checking the voltage of the signal line L (pin 1) of the alternator and when the ECU detects the abnormality, that information is sent to the CPU in the combination meter unit via the bus BEAN. The bus signal BEAN is decoded by the CPU and base of the transistor is controlled.

BaconMafia

Thanks for this info. Does this mean that if the ECU is not receiving anything from the alternator (eg. the connecter on the back of the alternator is unplugged), will the light not come on?

At this point, I am going to get small alligator clips and clip them onto the pins on the back of the alternator and run wire from the connector to the alligator clips. That way the alternator and ECU will be receiving the signals/power with certainty. If everything functions, then I will know that I screwed up the connector or pins when removing the connector and replace it. I will post the results of this.

Yamae

You can do that but be careful for the current draw. Without understanding it, you may damage the circuit. For examples, grounding the line may cause the excess current. Applying external voltage may cause a excess current. The current should be controlled precisely aiming not to damage the circuit. I only suggest the check to be done by a person who is familiar to circuits. I have seen many mechanics damaged circuits without knowing the problem caused by the too much current draw. Many of them are not skilled enough to handle delicate electronics circuits.

BaconMafia

SUCCESS

So I put a small alligator clip on the L terminal and hooked up a wire running from the connector to the clip. Low and behold, the battery light came on so I knew the plug was bad. For now, I bent the pins on the back of the alternator slightly and shoved the connector in will all my might and the system works like a charm. 14.4 volts at idle with accessories on.

Thanks guys for all your help. I appreciate it greatly. Moral of the story I suppose is if you have to spend this long and are lost on some electrical issue, it is something stupid and minor that you probably accidentally broke.

oldskewel

iTrader: (1)

Awesome success. Way to use your "mind and hand" to get it done, as my alma mater's motto says.