Yes It sounds like the voltage regulator inside the alternator has gone wide open .It can also ruin your battery and explode the battery.I would have it hooked up to a alternator tester and just to make sure it's not just your gauge.hope this helps
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Re: Alternator may be overcharging?
Well, 18 volts is an issue. And can cook your battery. Proper voltage range is 13.6 to 14.2 volts
The lower the voltage, the higher the amperage so 18 volts is doing nothing as far as charging but is doing alot towards ruining the battery. Have both checked. The battery could have wasted the alternator. good luck. I bet your battery needs lots of water. If so, it may already be trash.
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Test the alternator. The battery light is for the charging system. Once the charging system is working with the engine running, the light should go off. If your light stays on with engine running, the alternator may need service or replacement.
To test the charging system, just put a voltmeter on the battery with engine running. The voltmeter should register at least 13.5 volts- alternator is charging. If you only show battery voltage with engine running, like 12.2-12.8 volts, the alternator or charging system is not working. The battery light should be on to signify this.
If it is overcharging ( how do you know if the voltmeter is not working) then the problem will be either in the regulator of the alternator or the rectifier of the alternator. I would be looking at a blown diode in the rectifier allowing the alternator to produce ac current that will not work an voltmeter that is dc. The ac current is affecting the ability of the regulator to control the output of the alternator.
I think you are looking at the voltmeter, not the ammeter.
11 volts means the alternator is not charging if the engine is running. There are some conditions that exist in normal operation where the voltmeter can register 11 volts and it not be an issue, but if you are driving down the road, and only have 11 volts- the vehicle is running off the battery to keep the engine functioning for only a few miles more.
An ammeter in a car or truck has to be able to handle the full output of the alternator- which can range from 35 amps for some, up to 165 amps for others and higher. It is this reason ammeters in motor vehicles rarely have any numbers on them, just plus or minus sign, or the words charge discharge.
first and most important, check your oil level...make sure it is at full and is clear (not dark).
Your conditions normally suggest an electrical problem mostly seen if the battery and or alternator is not at full operating range. Try to get a digital voltmeter and measure the battery resting (not running), it should be about 12.4 volts or higher. With the engine running, it should read 13.9 to 14.7 volts. A cheap meter can be found for less than $10 and if you need to, go to a commercial auto parts store like Autozone, Advance auto or PepBoys and they will test your battery and alternator for free.
The alternator is vital part of your car
or truck's electrical system. When the vehicle is running, the
alternator provides a constant charge to the battery, as well as to
other accessories. Without the alternator, the battery will eventually
discharge. However, if the alternator isn't working correctly, it may
send too great of a charge to the battery, which is known as
overcharging. This condition is dangerous to your car's battery and
electrical system. You can test to see if the alternator is
overcharging, using a simple voltmeter.
Start your vehicle
and open the hood. Be aware of the moving parts within the engine
compartment, as you do not want to get your hands or tools anywhere near
Locate the vehicle's battery. It
may be obscured by protective shields, the air filtration or intake
system or a fuse box. Whatever the case, you need to remove everything
that covers the battery. You must have access to both the negative and
positive terminals of the battery.
Turn the digital voltmeter on
and adjust it to the proper settings, if necessary. The voltmeter must
be set to "DC" and 12 volts.
Connect the clamps or leads of
the voltmeter to the battery. You must connect positive to positive and
negative to negative. The positive lead is usually red or yellow, while
the positive terminal on the battery will be marked with a plus sign.
The negative lead on your voltmeter is black, while the negative battery
terminal is marked with a minus sign.
Examine the voltmeter. If you've
hooked it up properly, you should see a reading somewhere between 13.6
volts and 14.3 volts. A reading higher than 14.4 volts warrants further
testing by a professional. If your alternator is found to be
overcharging, you will need to have it replaced.
your car is fitted with PAS (power steering) when your engine is not running, the power steering pump will not function, thus making the steering heavy (feels like you cant move it, but you actually can, its just very very stiff and hard) when the battery light came on, and the steering went off, this is a sign that your ALTERNATOR (the battery charger) and POWER STEERING PUMP are on the same BELT, thus if the belt snaps, the light comes on and the steering gets heavy/stuck/hard.
You need to fit a new alternator belt as yours has more than likely snapped (common for all cars) and unless a new belt is fitted, you battery will go flat after a while too, as the alternator is the batteries power source (charger) when the engine is running! however the car will still drive/run, but i wouldnt advice it, as this will soon shorten the batteries power.
If you dont know how to fix it, you need to go to a garage/mechanic and tell them you need: A NEW ALTERNATOR BELT FITTING (they will charge for this service) this should then solve your problem!!
Hello! There is a Technical Service Bulletin (TSB) # 02-06-03-006B written that addresses this issue...Dated November, 2004...It concerns the way the battery cables are connected to the posts...Loose connections cause improper battery charging and intermittent starter cable continuity....The TSB mentions that the bolt that holds the cable connector in-place is either stripped or too long...The Bulletin also mentions the charging voltage...Running voltage must be greater than engine off voltage but less than 16 volts...A function of the Alternator...If the battery is leaking, the alternator is overcharging...Take the vehicle to an authorized GMC dealer and have the TSB installed if necessary...
You can check the battery cables (both - and +) for tight, clean connections...If you have a voltmeter, set it to read +12 volts...Measure battery voltage with engine off...Record reading...Start engine and measure again...Voltage must be 1.8 - 2.0 volts higher...In both measurements place the meter probes directly on the battery post and not on the connector...
what is the battery voltage with no headlights on and car running with a multimeter and your light on the dash on? what is the voltage at battery with car running and headlights on with a multimeter? It sounds like it is overcharging,
The reason it all goes circuslights could be that the alternator is overcharging.
The charge rate increases as the load and engine revs go up but only supposed to be a little, thats what the voltage regulator on the alternator is for.. when the regulator fails and alternator is overcharging eventually enough power is sent through the ground to light everything up and the computer cannot run properly.
High voltage levels cause sensors to read incorrectly so the computer cannot manage the engine.. Suggest you check out the charge cicuit at idle, at 2500 and at 3500 revs (briefly!)
Charge should be between 13.5 at idle, to 14.6 at 3500
Its a starting point for diagnosis.
Note that putting the alternator on a machine at Autozone will not necessarily pick up the fault - it needs to be checked ON the vehicle.
Hope this helps