Alternator light

I have an 8 year old Saturn with about 80k miles on it. The battery died awhile back, and a mechanic installed a new one and said everything else electrical tested fine. About two weeks later, my alternator light came on. I tested across the battery and it was putting out the correct voltage.

Now, the alternator light always comes on about 20 seconds after the car is started (when cold), and goes off after about 2 miles of driving. It reliably goes off, so is it a problem?


Something isn’t right. The alternator may be warning you of a more serious trouble coming on. The trouble could also be with the wiring to the alternator. With the age of your car you may want to consider replacing the alternator. I suspect it will correct the issue.

A weak diode in the internal rectifier can cause that. Sooner or later, the light will glow steadily and some other strange things may happen as the A/C ripple confuses the computer…

The way to test the alternator is to take it out and then to a shop or advance auto and run it on a tester there. You cannot test the regulator easily with the alternator in the car. The regulator is built in to the alternator and these days is not replaceable. The tester needs to spin the alternator and put a load on it to see if the voltage regulator can move enough juice.