Charging system failure

Tiny
HENRYR79
  • MEMBER
  • 2007 SATURN RELAY
  • 3.8L
  • V6
  • FWD
  • AUTOMATIC
  • 170,000 MILES
I changed the original spark plug wires, then started the engine, it revved it a few times then got a "charging system failure" notice on the dash display. The plug wire change out was a toughie since the wires were originals. I drove the van a little while and noticed the voltage dropped down to 13.2 volts. I pulled the alternator, had it checked at an alternator shop and was told it is charging fine. What could be the problem? Could my working on the plug wires, somehow have done something to cause this?
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Wednesday, January 18th, 2017 AT 4:54 PM

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Tiny
CARADIODOC
  • EXPERT
Testing off-vehicle is a very bad idea. No bench tester can run a generator like it is run by an engine, and none of the vehicle's wiring is included in the test. AC generators can easily require over five horsepower to run wide open. In-store bench testers rarely even have a one horsepower motor.

Also, do not rely on a dash gauge for accurate voltage readings. Those are only good for observing when an abnormal condition is occurring. You can start the testing by measuring the battery's voltage, while the engine is running, with an inexpensive digital voltmeter. It must be between 13.75 and 14.75 volts. Your observation the dash gauge was dropping suggests you are going to see that too with the digital voltmeter, and that points to a failing voltage regulator. That will not show up on a bench tester if it takes a few minutes to occur. Tests on the off-car testers are done and over in a few seconds.

If the charging voltage stays within the acceptable range, that means it is okay to do the second part of the tests, but that requires a professional load tester. Specifically, it is "full-load output current" and "ripple voltage" we want to see. Since the 1987 model year, GM has had a real big problem with their redesigned generators that develop huge voltage spikes. Those can damage the internal diodes and voltage regulator, and interfere with computer sensor signals. When one of the six diodes is defective, the most output current you'll be able to get is exactly one third of the rated current, and ripple voltage will be very high. 30 amps from the common 90-amp generator is not sufficient to run the entire electrical system under all conditions. The battery will have to make up the difference until it slowly runs down over days or weeks.

The battery is the key component in absorbing and damping the harmful voltage spikes, but it loses its ability to do that as it ages and the lead flakes off the plates. To reduce the high number of repeat failures, always replace the battery, unless it is less than about two years old, any time the generator needs to be replaced.

The place to start now is with the professional on-car charging system test. If the problem only occurs after the engine has been run a while, have the tests done at that time, not when the generator is still cold.
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Wednesday, January 18th, 2017 AT 5:41 PM
Tiny
HENRYR79
  • MEMBER
I tried to have the alternator tested on the before I pulled it, Auto zone told me the voltage was too low for them to test it and O'Reilly said they thought the voltage regulator was bad. That is when I decided to pull it and have an alternator specialist test it, which told me it was good. I wanted to make sure the problem was something other than the alternator by testing it alone.
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Thursday, January 19th, 2017 AT 4:32 AM
Tiny
STEVE W.
  • EXPERT
Take a large wire (I like to use a battery jumper cable) and run it from the engine block to the negative battery terminal. Start the engine and see if the failure goes away. It is possible you moved/broke one of the ground connections and did not notice. Also, check the wiring around where you worked. It is possible there is a connector that came undone or has failed.
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Thursday, January 19th, 2017 AT 9:54 AM
Tiny
MAXIMILIAM
  • ADMIN
I don't know what the problem was but I put everything back together and was going to use the jumper cable ground as you suggested I try, but after I put everything back together and started the car, everything is working fine now. I stopped the motor and restarted it several times and turned on all the electrical I could and it still works fine showing around 14 volts on my multimeter and the driver info center. Thanks for your ideas

Best Regards,

Henryr79
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Saturday, January 21st, 2017 AT 11:28 AM

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