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Discussion Starter #1
Hopefully simple>>>

The battery light came on last night near home. Just before I had noticed some occassional diming of headlamps momentarily. Today I started to drive and it remained illuminated. The belts all appear in good condition and tight. It spins the pulleys while running with no squealing. I checked the battery voltage and it was about 12.5v not running. When started, and running it drops to 11.8. Off it returned to 12.35 immediately. The fluid in battery is at the right level above the plates. The specific gravity is low approx. 1.2 and flirting between the Fair and Recharge line. Book says to trickle charge battery and retest. The battery is 3 1/2 years old. It runs long enough to charge battery when driving so Im thinking a charge is not the issue.

How can I measure to see if Alternator is working and giving proper output? Where should I sample with my voltage tester?

Thanks.
 

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The alternator light basically has to do with the alternator, not with the battery. Some auto parts stores will check both the alternator and the battery at no cost. An owner can do a quick check of sorts by measuring the voltage at the battery terminals using a voltage (VOM) meter with the engine off and then with the engine running. The voltage with the engine running should be higher than with the engine switched off. A charging system in good condition should put out about 14 volts, but if the battery is bad not all of that increase will register on the meter. And that sort of check only provides limited info.
 

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since you don't have a increase in voltage after it starts, and you have verified the belt is not slipping, and that all connections at the alternator are clean and tight, chances are the alternator itself, or the voltage regulator is toast.

Without a schematic in front of me I can't walk you through testing it ( stuff with built in regulators are hard to test as you can't read the field voltages) but my suggestion would be to rip it out and have it tested. You can go buy a rebuild at your local auto parts store and hope it works for more than a few months ( the quality of rebuilds out there really sucks, I am seeing failure after failure of parts) or you can find a good alternator/starter/electric motor rebuild shop and have them go through it, repair what is bad, and put the oem part back in
 

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Discussion Starter #4
Thanks. I was hoping it was just the battery acting up. They are relatively cheap and easy. I will pull it tomorrow and have it tested mor thoroughly.
 

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I can't tell you how many times I have gotten a call from someone saying their battery light was on so they replaced the battery and the light is still on.

If manufacturers put a pictograph of an alternator on the dash instead of a battery, people would be even more confused.

Our 4.3 RAV4 alternators are pretty bulletproof. Make sure you have 12 volts at the big fat wire on the back of the alternator. Also make sure all fuses are good. Disconnect the plug at the alternator, check it for corrosion and damage, plug it back in and see if the light is still on.

Normal charging system voltage is between 14.2 and 14.5 volts. A good battery should read 12.6 volts across the posts. (Each cell is 2.1 volts x 6 cells = 12.6 volts.)

If that checks out, then the alternator is probably faulty.

Extreme cold weather weakens a battery and then the extreme heat of summer kills it. I replace my batteries every 3 years so I never have to worry about it starting in the heat or cold. I get my batteries at cost, and my labor is free. Be especially careful that you buy the right battery, and that the positive cable goes to the positive post. It sounds stupid, but it happens. The clerk at the auto parts store hands you a battery with the posts reversed, and then you let all the smoke out.

Please don't buy an alternator at Auto Zone. I don't buy any parts for my vehicles there, and none of the mechanics at the shop do either.

If you can find a DENSO, that is OEM and the best you can buy. You will need to know where your RAV4 was built. The Japan built RAV4 has a different alternator than the Canada built RAV4. If your VIN starts with a J then it was built in Japan.
 
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not to go too far off topic, but right now almost all the rebuilt or reconditioned parts are done by the same company, and the failure rate is brutal.

as a tech I cringe because when they fail, I have to rip it out, fight with the supplier, and eat the labor on the R&R.

Most customers won't wait the 3 days it takes for me to send it out for a local shop to rebuild it, and I am lucky enough to have one close by and another about 20 minutes away.... on popular items they have them on the shelf, but Toyota (Denso) stuff is pretty reliable so finding them ready to go is rare, forcing us into using rebuilds, and I don't care if you are buying them from NAPA, Auto Zone, Advanced, or O'Reillys they are all sourced from the same suppliers if they are rebuilt reconditioned units.

I'd rather find a LKQ OEM part from the local junk yard than use most rebuilds.

OK rant over, good luck !
 

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My 'battery' light has been blinking erratically. Battery voltage is good and 13.9-14 volts when running.

50 miles and some more erratic blinking and I keep stopping and hoping the light will stay on to get an unusual volt reading running but no. At my last stop I got a running reading of 15.5 volts and the light did not come back on.

By the time I got home I could smell battery gas and was still getting 15.5 and no light. So the regulator is toast and the battery may be also. Top of battery looks wet. I ran the blower full blast and when I had to step on the brakes the blower RPM would go down and speed up again when I accelerated .

It's a little odd to me that the light would go thru that whole act but not come on for an overcharging situation. Maybe it burned out !!

Just writing this so others know not to ignore the situation just because the light has stopped misbehaving :)
 
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