Why is my car's battery light still coming on and off?

Question

About 3 weeks ago the battery light in my 92 Renault Clio came on and stayed on. I pulled over and sure enough my alternator belt had gone. So I got this changed and everything has been fine for about a week.

Now the light is coming back on again but not all the time. As a general rule, as I pick up speed the brighter and longer the light stays on. The belt doesn't appear to be slipping or at least I can't hear anything and it seems to be moving OK.

So has my alternator gone now and if so why is not showing a full light all the time?

Answer 1

Don't take the battery cable off while the engine is running! This is an old technique. The battery is an required part of the voltage regulator system. It also protects the computer, radio, and many other electric components from being destroyed in the event of diode failure.

The most common cause of the alternator light being on part of the time, or at varied intensity is a blown diode inside the alternator. The diode is like a 1 way valve for electricity. When it blows, it can stop power altogether, or allow it to flow both ways. If it is allowing the power to flow both ways then The battery is the only thing saving everything electronic in your vehicle from having the polarity reversed and being fried. It is grounding out the reverse polarity current.

The light varies in intensity because the voltage regulator cannot work properly because it is getting a reverse polarity signal 1/3 or 1/6 of the time.

I would have someplace test the alternator, and replace it if my theory proves true.

Answer 2

Check this out first: If with the engine running(the clamp needs loosened before hand though), you take the POSITIVE battery cable off of the battery and the car doesn't immediately die, then the alternator is good. If the car dies, then the alternator is shot. Plus, you may as well replace the battery, cables and alternator at the same time. See, most cars are very hard on alternators when the battery dies and is charged using the alternator instead of an outside charging device. When the car runs off of the battery alone, for some very weird(it's actually too long to explain here though) reason, the alternator goes bye-bye instead(if it hasn't already that is). The other thing that could need to be done is to have a mechanic shop or the dealership re-set the E.C.M. so the light stops blinking all the time. Check the alternator first though. I don't know of any parts stores that will charge you to check it. And while your at it, have them check the ignition module too.

Answer 3

it's a bit of a coincidence!
test the tightness of the belt by flattening your battery a ;little bit by having all your lights, fans, radio, anything else electrical on for about ten minutes before cranking the engine.

get a friend to crank the car and rev it in sharp pulses [hard blips on the accelerator] while you look into the engine bay at the alternator. if its a slipping belt, this will show it up

was the belt slipping/noisy before it broke? if so it could be that the voltage regulator on the back of the alternator has failed, causing high current at high[ish] revs high current would put a huge load on the alternator windings and the drive belt [the more current drawn the harder it is to turn the alternator round.

with the new belt, there is no slip so all the power is transmitted to the alternator, giving it no relief so all the loading is on the windings burning them - check if alternator gets hot!

bottom line - i agree with you, it's probably the alternator shot

Answer 4

Given that this problem started with the belt I suspect that it is belt related. There's a good possibility the belt is not tensioned correctly or when the belt broke off the first time, it took something with it (like a wire).

After that, the best thing to so is (beside visual inspection), get a cheap volt meter. You can get them from Radio Shack or Sears for as little as $20. Get the digital kind.

http://www.radioshack.com/product/index.jsp?productId=2103174&cp=&sr=1&origkw=digital+multimeter&kw=digital+multimeter&parentPage=search
http://www.sears.com/sr/javasr/product.do?cat=Electrical+Shop&pid=03482351000&vertical=TOOL&subcat=Multi-Meters%2C+Testers+%26+Accessories&BV_UseBVCookie=Yes

I have few meters but it seems like I often use the small one for the car.
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Measure the voltage at the battery (with the engine running). If it is about 13.8 V then the alternator is good. Now rev the engine high. If the voltage drops or rises +/- 1 volt then you have to suspect the alternator. What's happening is that your engine needs more and more electrical power for the ignition and can't supply it. So the voltage may drop (if the alternator is dying).

Oh by the way you can have them checked by sears or Autozone for free. But I don't always trust them because they have an interest in finding faults. I was once told to replace my MAF sensor by my Audi dealer ($280 job). I got a MAF cleaner for $5 and it did the job.


Good Luck

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Answer 5

When you had the belt off did you check the pullies to see if they spun freely? That is what I would check for just to make sure, then follow the other instructions except for removing the battery cable while the car is running. This puts undue stress on the alternator and could ruin it.

Answer 6

The alternator belt might not be tight enough either. The battery might be going bad, a loose connection some place. Check your battery cables and see if they are tight, they might also be corroded with acid. If so take them off and clean the battery posts and the battery cable ends.

Answer 7

sounds like the voltage regulator...you will soon no as your lights will get brighter bulbs will blow in the end....easy fixed just take to local rewind centre take 2 Min's to fit new reg....