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post #1 of 7 (permalink) Old 03-20-19, 02:02 PM Thread Starter
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Battery light comes on after 30 seconds

I have an ‘05 Mariner (V6). The alternator was not charging my battery (battery light on and alternator output would only go above 12 volts if the engine had high RPMs as measured with a voltmeter on the battery, the the battery light would go off).
Just got through replacing the alternator, and was happy to see the meter indicating 14volts and battery light off. However, after exactly 30 seconds, the battery light comes on even though the battery is still receiving 14 volts. Shut the engine off, start it back up, and EXACTLY 30 SECONDS later the battery light will come on, every time, even though the alternator output is good.

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post #2 of 7 (permalink) Old 03-20-19, 05:15 PM
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Re: Battery light comes on after 30 seconds

Check your belts and your connections.

Ever notice that there's so many high performance parts available for GM products?

Did you ever think that maybe they NEED them?
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post #3 of 7 (permalink) Old 03-21-19, 03:59 AM Thread Starter
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I have checked and rechecked them, all is good with them. And I have trouble seeing how a belt or connection would work for exactly 30 seconds, then fail on every engine start. And even after the battery light comes on (after EXACTLY 30 seconds), the alternator output is still 14+ volts (as confirmed by a voltmeter connected across the battery posts AND my scanner connected to the OBD connector).
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post #4 of 7 (permalink) Old 03-21-19, 04:16 AM Thread Starter
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I have checked and rechecked them, all is good with them. And I have trouble seeing how a belt or connection would work for exactly 30 seconds, then fail on every engine start. And even after the battery light comes on (after EXACTLY 30 seconds), the alternator output is still 14+ volts (as confirmed by a voltmeter connected across the battery posts AND my scanner connected to the OBD connector).
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post #5 of 7 (permalink) Old 03-21-19, 04:32 AM
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Re: Battery light comes on after 30 seconds

It's quite a common fault with many different vehicles that have the Smart Charge system , some examples and suggestions

https://fordtransit.org/forum/viewto...p?f=54&t=50183

https://www.rac.co.uk/forum/showthre...ectrical-Fault
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post #6 of 7 (permalink) Old 03-22-19, 08:25 AM Thread Starter
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I checked the voltage drop from the battery to the alternator small connector (pin 3), no voltage drop. Also verified 8 volts on pin 1 with ignition on, engine off. As far as the input circuit to the PCM on pin 2, I just checked resistance to ground since I couldn’t find a pin-out for the PCM. It was 6 megohms, and didn’t vary all shaking down the entire harness from the alternator to the PCM, so I had to assume it was good. Since the original alternator didn’t have the “after 30 seconds battery light” issue (remember, it just wouldn’t provide charging voltage unless I gave it 3000+ RPMs), I removed the newly installed “remanufactured” alternator and installed the original. Started the engine and gave it enough gas to get 13 volts to the battery. Battery light never illuminated. So the reman alternator had to be bad, right? I took it back where I bought it and explained all this to them, and they refunded my money. I then located a brand new alternator at another parts store and bought that one. Put it on, and it charged the battery with 14+ volts and no battery light. Problem solved, thanks for the input.
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post #7 of 7 (permalink) Old 03-22-19, 08:39 AM
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Re: Battery light comes on after 30 seconds

I didn't realise it was a reman alternator that was fitted . You can get so many problems with those units from different suppliers . With the Smart Charge system you are always better fitting OEM or at least a new unit . Thanks for updating the forum , hope that's your problems over .

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