Alternator: Troubleshoot

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Written by: 97mits3kgtsohc

How Can I Tell if my Alternator is Bad?[edit]

Personally when my alternator failed, my car's audio system turned off and all my lights faded but the car still drove. After pulling over and restarting the car, the car ran horrible (very boggy and will almost putt). To test if the alternator is bad, while the car is running, remove the positive cable from the battery. If the car instantly turns off then most likely your alternator is bad. If it stays on for a while, then your alternator might not be the problem. "Vr4god" from 3SI says If your car has a hotwired fuel pump then you cant disturb the positive cable that feeds to the pump from the battery or it will stop all power to the fuel pump and give you a false test. So take care and only remove the wires not associated with the fuel pump if yous is hotwired. My observation for my failing alternator was I would run at 13.5-14.0 volts at idle when engine was cold and or idling higher or if I gave it some acceleration otherwise at 750 rpm idle it would drop voltage all the time well below 11.9 volts with no powered items like AC, stereo or headlight on. You need at least 12 volts to your fuel pump and other electrical components such as the ECU to run the car properly plus it requires more than 13 volts while running to keep your battery charging while driving. If it drops below 12 volts you are running off your battery power only and it will eventually drain it and die on you like mine did at a very inconvenient place. Now you will require a jump start, eventually failing all the way. An aftermarket hotwired fuel pump requires a full 13.6 volts to adequately provide the proper amount of fuel to feed more fuel to your larger aftermarket injectors if you have them, this is the purpose of hot-wiring your fuel pump to insure a true 13+ volts to the fuel pump and to trickle charge the battery while driving the car to keep it charged. I also noticed my headlights would dim at idle and brighten back up once I started to accelerate again. I also had it tested locally and it was confirmed I had a bad voltage regulator and that friends is part of your alternator. It is cheaper to buy a re-manufactured alternator with a full warranty than to try and replace the parts yourself. I found by calling around the prices varied greatly on re manufactured alternators and brand new was well over $600.00 I bought mine for $117.00 from a well known part supplier with a GREAT REPUTATION while Autozone wanted $275.00 and both came with warranties. Some have lifetime others at least 3 years. So its worth calling around for the best prices and the best replacement alternator but these prices again are for a re-manufactured alternator. Any parts store can also test it for free if your experiencing any of the above symptoms.I could not even listen to my stereo as my voltage would drop to around 10-11 volts and that is way to low. So I replaced mine and now car is running perfect maintaining the proper voltage and no more problems.

Mel16m when my alternator began to go bad, dash lights started randomly coming on in my car, but when rpms increased, the lights dimmed, and almost went away, most auto parts stores now will test alternator for free

Seta8967 When I had this problem about a week before I had a issue with my battery dieing or what I thought was my battery. Then the night it died I noticed that both my battery and alternator light were on but very dim. soon after that my ABS, E-Brake, and SRS lights were on and my radio turned off. I removed the 40A battery fuse under the hood and put it back in to reset the connection and my headlights turned on. This made me sure it wasn't my battery.

  • I am hoping someone can edit what I left out or make this finer detailed.