Automotive

Alternator or Battery problem? (Light in dashboard dims in and out)

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  • Jan 5th, 2007 4:21 pm
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[OP]
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Dec 19, 2005
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Gatineau, Quebec

Alternator or Battery problem? (Light in dashboard dims in and out)

Turned on my car the other day and the Battery light in the dashboard appeared until I pressed on the gas and then dimmed out. It also seems to turn back on when I'm idling for a longer period of time (e.g., waiting at a red light) until I step on it, then the light dims again.

I noticed that the lights (speedometer) in my dashboard dims, which to me is a sign that I might be running on my battery rather than the alternator and that the battery is now starting to fail, but I'm not much of a mechanic.

Could it be that my alternator is weak and relying on the battery until I press the gas down enough to make it crank high enough? I was suggested to get it "re-timed" or something like that. I've never heard of that process but has someone in here?

Any thoughts or help?
The car is a '98 Hyundai Accent, two door, standard. About 180k KMs.
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You can check for a bad belt yourself , and if you have a digital meter , check the volts in the battery . Should be around 14 if the alternator is charging .
It could be the belt , battery , alternator .
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Dec 19, 2005
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Well I swapped the belt a few months ago, in August I think and haven't seen anything. I'll look again though. Battery's about a year old but I'll try to find a meter and check it out.

Does the old "unplug the battery while the engine runs" trick still work on newer-ish cars to check the alternator, or is that long gone?
[EDIT] Oh, and can the pulley be "used" up? Does that make any sense? I mean, a pulley either works or it doesn't, right?
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daedal wrote:
Dec 12th, 2006 2:19 pm
Well I swapped the belt a few months ago, in August I think and haven't seen anything. I'll look again though. Battery's about a year old but I'll try to find a meter and check it out.

Does the old "unplug the battery while the engine runs" trick still work on newer-ish cars to check the alternator, or is that long gone?
[EDIT] Oh, and can the pulley be "used" up? Does that make any sense? I mean, a pulley either works or it doesn't, right?
like he said, if you are getting around 14 when its running....... its not the alternator

also test the battery when its not running... should be 12 (11.5+)..... if its much lower, then its the battery :)
driving to NS to move, be back in a weekish
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I have never seen a car where a battery light indicated a battery issue, but rather a charging issue related to the alternator.

when the car is running it is not relying on the battery power at all, rather the alternator power, unless the electrical needs surpass what the alternator is able to supply (i.e. really big or poorly designed stereo). Only time I have seen something remotely close was a faulty cell in a battery putting a strain on the electrical system causing a really wonky idle.

I would put my money on the alternator without a doubt. If you're really curious, get it tested at the dealer, shouldn't cost more than $30. I'm sure Canadian Tire and the like can do a similar test.
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If you have a voltmeter you can do a quick test of the voltage across your battery terminals. Do this while the car is idling and you'll actually be testing the voltage produced by the alternator. It should be between 13.5 & 14.5v.

I'm not sure about cars, but on motorbikes there are electronics than can break & disrupt the charging system, eg., if a certain regulator goes then the generator will produce 19+v and that will fry the battery.

If it's lower than 13v while idling you definitely have a charging issue.

To test the battery, you have to charge it (i.e., use a known good charger) and then use a battery tester (most multimeters have one. This is different than a simple voltage tester). When the battery is fully charged it should read 13-13.5v on the tester. If you insist on using a voltmeter to test, it should be about 13.2-13.8v but even if you get that reading, your battery may still be dead since a voltmeter doestn' test the battery under load.
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daedal wrote:
Dec 12th, 2006 2:19 pm

Does the old "unplug the battery while the engine runs" trick still work on newer-ish cars to check the alternator, or is that long gone?

DON'T do it! It'll damage your car's computers.
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Jan 3, 2005
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Sounds like the alternator to me. The battery can easily be tested for free at Crappy Tire if you think that's an issue.

The reason the lights dim and brighten when you step on/off the gas is because the alternator turns faster when the gas is pressed, therefore getting the volts back up to where it should be.
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Alternator for sure!


DIY...it's easy, if you can get access. My RSX was a PITA.
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bembol wrote:
Dec 13th, 2006 4:37 am
Alternator for sure!


DIY...it's easy, if you can get access. My RSX was a PITA.
Yeah, I'm sure I can manage the swap. The only thing I hate about swapping out an alternator is the damned belt. I'm not too mechano-inclined but I can do most swaps without a hassle. Called a few places. Best price I found is 211$ if I return the core, which I will.

I'll check it out and see what's going on. Thanks for the feedback guys, I really appreciate it.
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[OP]
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Took me a while to post back but I did end up checking the battery and it's seems to be in great shape (always at 12v minimum) and the laternator seems to be doing it's job at around 14.5v when it runs.

Here's the weird thing about it: yesterday, I come home and finnaly get a couple of minutes to check the car. I started by cleaning the connectors and terminals and then proceed to checking out the system with the voltmeter. Everything runs great. Battery's good and the alternator's doing it's job so I figure it may have been dirty or loose connectors and that I must have solved it.

Later on, I drive down to the store. No problems. Coming out of the store though, I turn on the car and the Battery icon lights up in the bashboard. I give a bit of gas and it diseappears. I speed home fearing that I might be running on battery power (didn't have my voltmeter with me). Once home, I pop the hood and run the same tests. The battery is still at a clean 12v line. I turn on the car though and the Battery light comes on again. I check the battery now which should be around 14ish volts but it's still at 12v so I give it a bit of gas and it shoots back up to 14.

What could be causing this? At first I thought the strap might be loose but since I was in the dark last night (and didn't have a flashlight handy) couldn't check it out but why would the alternator not kick in until the engine revs?

A similar problem occured when the car idled at a red light for example. The brightness of my dash would dim until I gave it some gas. Almost like the alternator was underpowered at low RPM?

Totally clueless here guys. What are your recommendations? I'll check the belt tonight and see if there's any extra loose but I don't think it'd be the cause of my problems.
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Sounds like a poor ground. Have you installed anything lately (stereo amp)? A poor chassis ground somewhere can make the light come on and then go dim when rpms increased. Also, the regulator can be going, these are sometimes external to the alternator depending on the age and type of car you have. The battery itself should always be at 12 volts. The alternator output should be around 13 to 14 volts.
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Pete_Coach wrote:
Dec 21st, 2006 2:04 pm
Sounds like a poor ground. Have you installed anything lately (stereo amp)? A poor chassis ground somewhere can make the light come on and then go dim when rpms increased. Also, the regulator can be going, these are sometimes external to the alternator depending on the age and type of car you have. The battery itself should always be at 12 volts. The alternator output should be around 13 to 14 volts.
The only poor ground I can think of is the speaker grounds of my two rear speakers which are currently disconnected (e.g., wire hanging out) but I don't think that could cause an issue, could it?

The car itself a a '98 Accent, SOHC.
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Based on the symptom you described it looks like your alternater is on the way out.

Battery should read 12V when the engine is off and about 14V when the engine running. If you have to give a bit of gas to "kick" the alternator this means the alternator is weak. The dimming behaviour further confirmed this.

I think CT or PartSource can bench test alternators. Give them a call.
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Dec 2, 2003
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Your alternator isn't dead, but it soon will be, change it before it causes you a problem.

PartSource will bench test alternator for free (and they usually have half decent prices).
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