So I was driving home from school a couple days back and as I was driving in traffic my car's VSA indicator light and the VSA warning light (yellow triangle) came on and my car began to stay at a constant RPM around 1500 and I couldn't get it pass about 2300. I kept giving it gas but it just wouldn't go and I eventually had to pull off to the side of the freeway. I turned it off and then tried to turn it back on but no luck. Does this mean my alternator is done or could it have just been my battery? When I got it home and tried another battery it started right up? The exact same thing happened to me before but that was because I ran out of gasoline. Any help would be appreciated.

Thanks,
Arthur

 

The most effective way to diagnose battery and alternator problems is with a voltmeter. Take a reading after it sits overnight - should be 12.5v or better. Low voltage here suggests bad battery. You can also watch the voltage at the battery while cranking the starter - it may drop to 10.5v or so; a little higher is better, lower says you have a dead (or discharged) battery.

While running (even idling) it should be over 13.5 and may go as high as 14.5 at speed. Voltages outside this range (usually low) suggest alternator problems.

If you don't have a volt meter, spend $10-20 at a place like Radio Shack and get one.