This is typical of a charging system problem, specifically worn brushes inside the generator creating intermittent connections. This type of failure happens on any brand of vehicle with higher mileage. Your mileage is not really that high yet, so we might end up looking for bad connections in other places if a replacement generator does not solve the problem. With worn brushes, the symptoms will occur more frequently and for longer periods of time as time goes on.
There are other forms of generator failure that are extremely common on GM vehicles since they were redesigned for the 1987 model year. Due to that design, they develop huge voltage spikes that can damage the internal voltage regulator and diodes, and interfere with computer sensor signals. The battery is the main component that dampens and absorbs those harmful spikes, but as they age and the lead flakes off the plates, they lose their ability to do that.
It is real common to go through four to six replacement generators in the life of a GM vehicle due to these voltage spikes damaging the replacements. To reduce that number of repeat failures, always replace the battery at the same time, unless it is less than about two years old. The old battery will work fine in an 1986 or older model.
Diode failures are rarely intermittent. When one shorts, it stays shorted. Voltage regulators can be intermittent, but if that failure is caused by a voltage spike, that will be a permanent failure. Since your symptoms are intermittent and the charging system resumes working at times, I am leaning toward worn brushes. It is not practical to try to replace the brushes. That is an easy and inexpensive job on most other brands, but GM's generator was not designed to be taken apart or repaired by competent do-it-yourselfers. Even most mechanics will not attempt it. The diode block is usually destroyed by trying to unsolder multiple wires to it at the same time, and once the assembly is apart, there is no way to test the individual parts, so to avoid going through all this work a second time, you will want to replace every part that could fail. You will find buying a professionally-rebuilt generator with a warranty is a much better value.
Here is a link to a guide that explains how to test the charging system:
https://www.2carpros.com/articles/how-to-check-a-car-alternator
This can also be done by your mechanic with a professional load tester. The tests only take a minute, but it is important to understand any testing has to be done while the problem is occurring. You do not want your mechanic to wander around waiting for that to happen, so this is easier done yourself with the voltmeter.
Do not worry about the multiple warning lights. Those are symptoms, but not clues related to this problem. The lights you listed are for systems that are run by computers, and those systems draw high current at times. The computers know they will not be able to function properly with low system voltage, so they turn their systems off, and turn the warning lights on to tell you. Once the charging system problem is repaired, those warning lights will turn off and the computers will go back to normal operation.
Here is a link to an article about generator replacement if you want to do this yourself:
https://www.2carpros.com/articles/how-to-replace-an-alternator
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Tuesday, November 6th, 2018 AT 1:15 PM
