2002 Chevy Cavalier Battery, Alternator or Wiring?

Hi mijolkause. Welcome to the forum. Your mistake is the last comment, "why does it keep dying?" Since it works fine for up to three days, you have an intermittent problem. You'll have to do any testing when the problem is acting up. You should see the red "battery" light turn on when this happens. Lights will dim and the heater fan will slow down. During that time, battery voltage should be measured with an inexpensive digital voltmeter. You must find between 13.75 and 14.75 volts with the engine running.

Worn brushes inside the generator are a real common cause of intermittent output. That would be a typical reason for the unit to work properly when you took it for testing but it quits working three days later. Left alone, it will start acting up more often.

Another potential intermittent problem is a poor connection on the instrument cluster connector. When the generator stops working, measure the voltage on the small red wire that's plugged into the side of the generator. You should find full battery voltage there, (12 volts or more). If you find very low voltage AND the warning light is on, the generator is not working. If you find low voltage and the light is off, there is a break in that red wire or circuit.

Caradiodoc

You have an intermittent problem. Those can be terrible to find. You have to troubleshoot only while the problem is occurring. Worn brushes inside the generator are the most common cause of intermittent operation but other components can cause that too. GM, in particular, has a huge problem with their generators ever since they redesigned them beginning with 1987 models. It is fairly common to go through four to six of them in the life of the car.

Your generator also uses an internal voltage regulator. One of its jobs is to turn off the warning light. That part could be working but the part that runs the generator itself could be intermittent.

There are only two wires on the generator you need to look at. When battery voltage drops below 13.75 volts, (engine running), measure the voltage on the large wire bolted to the back of the generator and the small red wire plugged into the side. If you find very high voltage on the large wire, ... Say 15 - 18 volts, there is a break in that wire where it goes back to the battery. That is pretty rare. The red wire should have a low voltage but not zero. Low voltage means the warning light is on and that little voltage tells the voltage regulator to turn on and do its thing. Once the generator is working, the voltage on that wire will go up higher to turn the light off.

A break in that red wire makes it look like the ignition switch was turned off so the generator turns off too. In that case, you'll find 0 volts on the red wire. The most common place to find an intermittent break is in the electrical connector for the instrument cluster. Current has to go through the two circuits for the warning light to get to the generator.

You can find an inexpensive digital voltmeter at Sears, Radio Shack, and most department stores. If you have a Harbor Freight Tools store nearby, they have one for $6.99 that goes on sale sometimes for as low as $2.99.

Caradiodoc