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Old 08-02-2009, 07:25 PM   #1
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Please help. Replaced alternator, new battery, Battery light still on

Hi everyone, I'm in desperate need of advice.
My alternator went out on me the other day and drained the battery.
I replaced it with an alternator from Advance Auto and also got a new battery.

The battery charge light is still on and is causing idle problems between 500-750rpm and causes it to just shut off.

I also recharged my dead battery and tried both new and old batteries

Both batteries tested at 12.66 and 12.87 Volts.

I have checked for the connection grounding and it all seems fine

Battery terminals are also clean and okay.

Please help!
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Old 08-02-2009, 07:27 PM   #2
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Did you let it run for awhile or take it for a drive?
Since the battery was disconnected for a good period of time, the PCM reset the fuel trims and they need time to relearn (usually a couple drive cycles).

Also, did you measure ~14.4V from the alternator while the car was running
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Old 08-02-2009, 07:54 PM   #3
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yes drive it a while and you will see a miracle!
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Old 08-02-2009, 08:48 PM   #4
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Make sure that your connection to the Mass Airflow sensor is still hooked up. If the MAF isn't reporting any voltage to the PCM it will trigger a battery light and a check engine light. The car will still idle as it will assume there is 8 grams of air incoming and apply the appropriate amount of fuel.
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Old 08-02-2009, 08:52 PM   #5
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Quote:
Originally Posted by Flashwing View Post
If the MAF isn't reporting any voltage to the PCM it will trigger a battery light and a check engine light.
An absence of a signal/voltage from the MAF can trigger the battery light?
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Old 08-02-2009, 09:00 PM   #6
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I have driven it for another day, perhaps tomorrow it will disappear. I will probably have the dealership look at it tomorrow if it doesn't disappear after my drive from work.

I will go check the MAF sensor connection, as well as fuses.

I'm afraid it was because didn't buy an OEM mazda alternator

I'll keep u guys updated. Thanks
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Old 08-03-2009, 10:13 PM   #7
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I have a feeling that the stealership is trying to full a fast one on me.

After being diagnosed, i received an engine code of P2503 which states of the charging system voltage being low. ALONG WITH B1342 code which claims to have ECU internal fault.

They say that this ECU/PCM is causing the battery light to go off and needs to be replaced. $881 for the ECU and 3 hours of labor to install it.

I called another Mazda dealership and only quoted be one hour to install the PCM, reflash it, and sych it with the key fob.

Anyways, the alternator was read at 13.87 Voltage charge, while all the batteries tested okay.

I bought an OEM Mazda alternator and will install it tomorrow. I bet it will fix it.

Has anyone had a problem with a non-OEM alternator in the past?
I know these alternators from advance auto are all refurbs.
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Old 08-04-2009, 09:37 AM   #8
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Just replaced the refurb alternator with an oem. Fixed the problem. Using oem parts is a new lesson for me. Turns out other alternator didn't charge above 14v
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Old 08-04-2009, 09:47 AM   #9
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same thing happened to me. just reset your ECU and all should be well.
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Old 08-04-2009, 09:55 AM   #10
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i got my alternator from auto zone and i've had no problems with it and i've had it for about 9 months.
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Old 08-04-2009, 10:00 AM   #11
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Quote:
Originally Posted by turbonetics-g View Post
Just replaced the refurb alternator with an oem. Fixed the problem. Using oem parts is a new lesson for me. Turns out other alternator didn't charge above 14v
stock alternator should output around 14.2-14.4 under all conditions.

so if your old one charges below 14v, yes it has a problem.
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Old 05-27-2011, 04:14 PM   #12
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I'm having a similar problem. I replaced the battery and new alt.; not rebuilt, and the battery light stays on. The CEL came on a few days ago so I took it to the dealer today. They reset the PCM, and the CEL went out but the bat. light is still on and they have no idea why. The charging system checks out ok.

Any opinions?

Thanks in advance.
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Old 05-27-2011, 04:45 PM   #13
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Did they get a code for the CEL? Or just reset it and hope it doesn't happen again?

On the alternator... The alternator light (mislabeled BAT on too many cars) essentially goes on when current flows from the battery to the alternator instead of from the alternator to the battery. I don't know if today's alternators are like this, but some time ago I had a car where the charging system functioned perfectly OK but the alt light was always on. Besides the main output diodes, there was a small "diode trio" kind of on the back side that got into the act. The dealer replaced that once during the one year warranty, and a couple of years later I replaced it myself.

Anyway, it needs someone who understands the electrical system, not just someone trained to put a tester on.

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Old 05-28-2011, 07:49 PM   #14
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I'm not sure if they read a code or not, but I'd assume they did because the service writer said everything checked out. But their reason for me bringing it in was to reset the PCM, so maybe not. I'll have to ask next week when I take it back.

I'm really concerned that it may be fault in the ECU. I understand that is a costly repair!

Great point about finding a charging system expert, because you're right...some technicians only know what the readout tells them.

Thanks Ken for your input.

Fred
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Old 06-25-2011, 12:16 AM   #15
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No code was displayed, so everyone was scratching their heads. I left it and they let it run with the test equipment on it for two hours and they said it stayed at 14.5 volts the entire time. When I got there the mechanic said, see nothing wrong like I said; look...I'll show you! So he turned it on and it read 10.0. More head scratching and stuttering. After swapping out the new alternator for another one, the battery/alternator light went out. Problem solved.
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Old 06-25-2011, 12:16 AM
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