My Mechanic has given UP - Excessive Alternators and Batteries

Over last two years have replaced a few alternators and (3?) batteries in my 2000 Solara SLE with 150,000 miles. However, In last three months I have had three additional alternators. Car wouldn’t start, had it towed, and a mechanic put in new alternator and battery. Happens again, car won’t start (now own a jump charger!), and the same mechanic puts in new alternator. Happens again and Mechanic #1 says he has checked it and its fine. I then go to my regular mechanic… Says its the alternator which is bad (when you put the AC and Radio on, it appears to charge for a while, but if you leave it running it will stop charging and then after a while it will go to overcharging and undercharging. I noticed when driving on highway my lights will brighten and dim). He sends me back to the first mechanic because the alternator is bad. They put in a new alternator. I take it back to Mechanic #2 my regular mechanic to test it so I don’t get stuck. He says its still doing the same thing. I tell him I will pay to have him put in the new alternator and he can own the warranty… He sends me to a car electrical specialist. After having my car for 3 days the car electrical specialist just called and said in 30 years he has never given up but he has now.

May or may not be related: My check engine light was coming on and I had mechanic put in new oxygen sensors. I also have intermittant traction light and ABS light coming on and the check engine light will sometimes come on too. My dash board feels like Christmas…

I suspect what might be going on is the battery sense lead to the alternator has excessive resistance in the connection between the battery and the alternator. That will cause the voltage regulator to think the battery voltage is low even though it is okay and over charge the battery. That will cause excessive duty for the alternator and could make it fail faster than it should normally. There should be very little difference in voltage between the positive battery post and the sense connection to the alternator if that wire is ok. If there is a voltage drop there then it means there is a resistance in the line that shouldn’t be there. The tech should check the charging current while the battery is fully charged and there are no accessories turned on. The charging current should be pretty low then. If it is high then the regulator thinks the battery is low on charge and that makes the alternator work when it shouldn’t be.

Another possible trouble is a high resistance between the alternator output and the battery. Voltage between those points should be under .3 volts with a good load. The same goes for the alternator case and the ground post of the battery. Hopefully the battery post clamps are in excellent shape.

Many good mechanics can get blown out of the water dealing with electrical problems. It is often worthwhile to find a shop that specializes in electrical work and if the first was not successful find another.

Clean or tighten all the grounds. Engine to body is a good one. There are some under the dash, maybe at the top of the carpet. It may not help but you could get lucky.

I agree with all the comments. One thing I do is to add a ground cable from the engine to the frame and one from the engine to the vehicle body if I run into any quirky electrical problems. It isn’t 100% effective but it sure solves a lot of the problems and cuts down greatly on the troubleshooting time.

Another possibility is if the voltage regulation is done in the ECU (computer), that there could be a problem with that. A poor connection somewhere is what I would check first, but a flaky ECU could cause these problems too. I would also check the connector to the ECU for corrosion, water intrusion, and general fitness. I think the warning lights you’re getting are due to the voltage fluctuating so much–the electronics and sensors that handle the traction control and ABS need a stable power supply to work right. I have experienced the same problem you have with the ABS and TC lights coming on when I had a poor battery connection on one of my cars.

I’m also curious as to how all the previous alternators were determined to be bad. If proper charging voltage was just checked with the car running, it could look like a bad alternator, but be another problem. Hopefully they were bench tested instead, or at least some of the ‘bad’ alternators may have been perfectly fine. Hopefully the batteries that have been so frequently replaced were load tested as well, instead of just assuming that they’re bad because “it has to be one or the other”

When I read this post, my first thought is a problem with the voltage regular part of the charging system. As @Cougar mentions above. My second though is a question: Are these alternators that are being installed new ones from a dealer, or aftermarket rebuilt ones? If the latter, consider to invest in a new OEM alternator. There’s been quite a few complaints here about faulty aftermarket electrical parts – esp starters.

In any event, the lights brightening and dimming is a major clue, should be measurable, and any good auto-electrical expert should be able to at least determine what the problem is. I’m not saying this diagnosis will be inexpensive, but it is certainly possible to fix this problem.

I might suggest (and I’m assuming the belt and tensioner is good) the problem may be in a fusible link in the charging circuit between the alternator and battery.

This car should use the varying color coded based on amperage links which plug into the underhood fuse/relay box.

Sometimes with age and miles the connectors burn or corrode or as more often than not, the heat from the high current will melt the solder inside the link which in turn cause a poor connection.
The links should have a clear plastic cover on them and with a careful eyeballing, sometimes the solder may appear to balled up at the end the wire. Any balled up solder means the link is failing and connections can be intermittent due to the solder melting and then cooling off again.