Intermittent battery light on

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tjrob2000
Posts: 100
Joined: Sat Jun 07, 2014 5:42 pm
Car: 2007 G35 sedan (journey)

Re: Intermittent battery light on

Postby tjrob2000 » Tue Dec 15, 2020 6:57 am

Look, I'm not trying to start an argument I just don't buy that a charging system would be designed to not work for the first 8 miles you drive it. That simply doesn't make any sense. How would a mechanic troubleshoot that unless they first drive the car 8 miles? Why would an engineer design a system that runs entirely on the battery for the first few miles instead of putting that load on the alternator where it belongs? The batteries in cars are starter batteries, not run batteries (may not be the correct term, but you get the gist), meaning their sole purpose is to start an engine verses carrying the load of running it and all accessories.

I don't doubt that if you take away the control signal then your alternator will always be at max output, provided all else is working correctly and that's fine. Personally I'd rather find the root cause of a problem rather than just trying some workaround, but I understand that isn't always possible (I work in the technology field so I know how difficult finding root causes of problems can be and that sometimes the workaround is what you need to move on).

Anyway, as I've said, we'll see if this latest alternator and the new tensioner are the fix for my car or not in time.


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VStar650CL
Posts: 1616
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Re: Intermittent battery light on

Postby VStar650CL » Tue Dec 15, 2020 7:09 am

I'm afraid you're not getting it. It isn't "designed" that way. There are a small percentage of vehicles that simply don't perform as "designed". Secondly, it doesn't put the alternator on "max output", it causes it to go on internal regulation. That means it outputs 14V regulated output like any car without "smarts" in the charging system. It doesn't mean it stops regulating and over-charges the battery.

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VStar650CL
Posts: 1616
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Re: Intermittent battery light on

Postby VStar650CL » Tue Dec 15, 2020 7:18 am

PS - On the few cars where we've replaced the IPDM, it was a crapshoot whether that actually resolved the problem. There seems to be some sort of intricate loop between the IPDM, current sensor, and voltage sensor in the system. Since the problem has persisted across multiple platforms including the new Armada, I think it must be some sort of "cumulative production tolerance" issue that's resisting finite analysis.

tjrob2000
Posts: 100
Joined: Sat Jun 07, 2014 5:42 pm
Car: 2007 G35 sedan (journey)

Re: Intermittent battery light on

Postby tjrob2000 » Tue Dec 15, 2020 7:59 am

VStar650CL wrote:
Tue Dec 15, 2020 7:09 am
I'm afraid you're not getting it. It isn't "designed" that way. There are a small percentage of vehicles that simply don't perform as "designed". Secondly, it doesn't put the alternator on "max output", it causes it to go on internal regulation. That means it outputs 14V regulated output like any car without "smarts" in the charging system. It doesn't mean it stops regulating and over-charges the battery.
My apologies if I misunderstood the way this fix has been described. The video I saw states the system doesn't charge for 8 mile, which makes it sound like they are saying it's designed that way. Thanks for your clarification. Also, I didn't mean to imply it would over charge the battery. I understand the disconnecting of the control signal just makes it no longer a smart system. I appreciate your input and I've wondered about the IPDM being a possible cause (and perhaps it still is). If it pops back up then I'll try this fix.

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VStar650CL
Posts: 1616
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Re: Intermittent battery light on

Postby VStar650CL » Tue Dec 15, 2020 9:55 am

tjrob2000 wrote:
Tue Dec 15, 2020 7:59 am
My apologies if I misunderstood the way this fix has been described. The video I saw states the system doesn't charge for 8 mile, which makes it sound like they are saying it's designed that way. Thanks for your clarification. Also, I didn't mean to imply it would over charge the battery. I understand the disconnecting of the control signal just makes it no longer a smart system. I appreciate your input and I've wondered about the IPDM being a possible cause (and perhaps it still is). If it pops back up then I'll try this fix.
No worries, no apology needed. The problem is, IPDM's are expensive and no one can say whether it will fix the issue. The determinate "voltage reading" comes to the IPDM from the ECM via CAN, and the current consumption on most versions similarly comes from the BCM. The alternator doesn't directly report its output a la Ford, the ECM and BCM need to infer its performance from the sensors. So there are multiple possible error sources. For the engineers, chasing a finite analysis is a bit like the old Peter Principle corollary that if more than one person is responsible, no one will be at fault. Chances are it's an issue called "cumulative tolerance", where the +/- tolerances for all the components cancel out on average, but a small percentage of vehicles have components that are all off in one direction and add up to a problem. Like I said, the issue has spanned many years on many models, so if there was an easier answer they would have found it long ago.


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