QuestionI have a 2002 sonota, 2.4L. Battery light came on on Friday. Pulled altenator and battery on Saturday, both tested fine. Sunday after driving for approx 1 mile and then idleing for approx 10 minutes, came back out to car and headlights were dim, gauges didn't work, signals, etc, car drove like it was running on the battery and alt. Took battery and altenator off vehicle again, to a different store and both tested fine. Even put alt through 10 back to back tests and all passed. I put everything back in and checked grounds and belt tension and all appear fine. Drove it again last night for appoximately 2 miles with no issues, but not confident problem is fixed since I didn't replace anything.
AnswerAlternators will sometimes fail to charge properly when they get hot. Most likely, that's what is happening here. By the time you get it off the car and take it to the store, it's working properly again.
If the problem occurs again, try to check it yourself while the problem is occurring as follows:
With the engine running, verify the alternator belt is turning the alternator pulley. I fnot, you may need to tighten the belt.
Unplug the alternator connector and check for voltage at the two center terminals. With the key on, the orange wire should have battery voltage. Also with the key on, the gray wire should also have voltage, but it may be as low as 7V or so, because this is the circuit that operates the battery lamp. If you don't have the proper voltage, you need to check for an open circuit in the orange wire or a short in the lamp circuit going to the gray wire.
Since the alternator controls the battery lamp, the only way for the lamp to come on is for the alternator to turn it on or for there to be a short in the gray wire circuit. If you have all the proper inputs to the alternator and its pulley is turning, then the problem lies within the alternator itself.
