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I was driving along and got a check gages light on. Then my voltage went down to 8 volts. Got home and tried to start but no go. Checked battery voltages both at 8 volts.
I cleaned the terminals and charged the batteries. It started and now i have a check engine light on. Took truck in and got a scan done.
Found a message that said
“96 over/under voltage.
Started the truck and it started to charge at 12.7 V shortly after it started the voltage went up to 14.99.
Looking to find out what that message is telling me.
Thanks
 

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Sounds like your alternator/ voltage regulator is intermittent. The normal range for a "good" alternator voltage is ~13.8-14.5 . Check this with a good volt meter rather than the gauge in your truck. Less than 13.8 will cause very long charging times. More than 14.5 could cook your battery and drastically shorten it's life. If your voltage is reading much more or less than that it is probably time for a new alternator. But before you open your wallet, it's a good idea to check all your battery and alternator connections. A simple loose connection could cause the alternator to fail to produce good voltage.
 

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I was driving along and got a check gages light on. Then my voltage went down to 8 volts. Got home and tried to start but no go. Checked battery voltages both at 8 volts.
I cleaned the terminals and charged the batteries. It started and now i have a check engine light on. Took truck in and got a scan done.
Found a message that said
“96 over/under voltage.
Started the truck and it started to charge at 12.7 V shortly after it started the voltage went up to 14.99.
Looking to find out what that message is telling me.
Thanks
It looked like a BAD electrical connection at the passenger side positive post since both batteries were under charged and there was no sign of overcharge on the passenger side battery.

The system target voltage depends on the drive side battery temp which in turn depends on the ambient temp.
And the max target voltage is 15V, so 14.99V is within the range.

Just make sure both batteries see the same voltage while charging by measuring the voltage drop across the two battery positive posts. The voltage drop should be close to ZERO.:wink2:
 

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I use a scan gauge with the latest firmware (it has tranny temp, highly recommended), and voltage displays all the time, mine is 14.2-14.3 almost always with an occasional 14.1. Point is, it’s a good idea to get something that shows the output since the stock gauges are not always reliable. This way I can notice the dipping asap if there is a problem.
 

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I know this is an older post, but as I was searching the site this post seems to best match my situation.

I have a 2004.5 2500 and I installed a 220A alternator from a fourth gen this weekend. I changed the terminal block from fourth gen to third gen (thank you @KMech) so the factory wiring would stay intact.

The alternator to battery oem connection was in really bad shape, so I made up a new one using #2 wire. All connections at the passenger side positive terminal were cleaned and reconnected. The plug that connects the harness to the alternator field will also be replaced soon as it is in rough shape.

Once running, the alternator is charging right at 15 VDC. This is measured at both batteries with a Fluke 87. The voltage has never been this high ever before and I am concerned. I drove the truck for an hour taking voltage measurement with the DMM along the way and it remained steady at 15 VDC. I will add that the temperature has been in the low 20’s as I’m going through all this.

I removed the 220A alternator and took it and the 136A alternator to the local parts store to be tested. They both passed all tests. I reinstalled the 136A alternator and nothing changed: the truck is still charging at 15 VDC.

The only things that changed is that some connections were cleaned, a new alternator to battery cable was installed, and the plug that controls the alternator field was disconnected and reconnected a few times.

Has anyone had this issue? Is it possible the field connection was less than ideal before I cleaned everything up and now it’s where it should have always been? Can the max charge voltage be dialed back with a programmer?

Thank you all for your time.


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The ECM dictates at what voltage the batteries are charged at. I also did this swap and found that after the swap I never saw 13V again like with the 136A alternator indicating to me that it was on its last leg (420k miles or so).

15V is OK as long as its both batteries getting the same current. I had a crossover cable fail & fried the PS battery. Swapped in a new cable from Napa that came with the Alt cable and all was good up until last week. The fried battery started leaking acid up into the new cable and corroded it pretty quick. Out went that battery, cleaned it up again and in went a new battery. All is good now.

In HP Tuners I can dictate what voltage the batteries run at, I lowered mine some down to 14.6 and it runs at 14.7 via the obd port.
 

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To the collective: is there a way to view what the ECM is reading and what it’s providing to the field winding?

I can measure the voltages at all points external to the ECM, but I’d like to know what the ECM thinks it’s seeing and what it’s set point is. That would at least provide some idea of what it’s doing.


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You can read the voltage off the odb ii port with a scan tool.

To see what it's commanding vs actual I imagine you need something like HPTuners device + software. I never logged it but believe I can with mine.
 

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To see what it's commanding vs actual I imagine you need something like HPTuners device + software. I never logged it but believe I can with mine.

This is exactly what I’m referring to.

What system are you using and if you had to do it again would your choice remain the same?
 

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To see what it's commanding vs actual I imagine you need something like HPTuners device + software. I never logged it but believe I can with mine.

This is exactly what I’m referring to.

What system are you using and if you had to do it again would your choice remain the same?
I have the MPVI2 + tunes from FP which is mainly what I purchased it for. I have to run out to pick some stuff up but I'll try and remember to get it hooked up later tonight and confirm it does that.

That said, lot of money if that is all you wanted, but it logs a lot, way more than most monitors or torque pro can see.

HP tuners is the way to go on the trucks that don't support EFI Live or if you want to tune yourself. I'm definitely happy with it, but it mostly sits in my desk drawer. Needs a laptop currently still far as I know, so would have to take my laptop everywhere. It's more for datalogging issues that come up than running everyday monitoring at this point since tunes are done.
 

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I have the MPVI2 + tunes from FP which is mainly what I purchased it for. I have to run out to pick some stuff up but I'll try and remember to get it hooked up later tonight and confirm it does that.

Thank you

Do you have the “Pro” version that permits the additional analog data logging?
 

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I have the MPVI2 + tunes from FP which is mainly what I purchased it for. I have to run out to pick some stuff up but I'll try and remember to get it hooked up later tonight and confirm it does that.

Thank you

Do you have the “Pro” version that permits the additional analog data logging?
It has the ability to do analog data logging. I've never messed with it.

Pictures below of what HPTuners shows. The graph is what the stock tune is set too. I'm guessing my FP tune is a little higher based on the control module voltage being higher than Max of the stock tune.

So it's based on battery temp. I can't remember if torque can read battery temp and forgot to look while I was messing with stuff.

Hope this helps.
 

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Thank you for helping me along the troubleshooting path by taking time to share your knowledge.

I’m viewing this forum from an iPhone and I can’t see your pictures.

I have observed over time that the HP tuner route makes sense from both an initial cost and from a DIY perspective. I will likely go down that road soon.

Tomorrow I will go over all of the mechanical connections (clean/torque) and test the temperature sensor.
 

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Thank you for helping me along the troubleshooting path by taking time to share your knowledge.

I’m viewing this forum from an iPhone and I can’t see your pictures.

I have observed over time that the HP tuner route makes sense from both an initial cost and from a DIY perspective. I will likely go down that road soon.

Tomorrow I will go over all of the mechanical connections (clean/torque) and test the temperature sensor.


Sent from my iPhone using Tapatalk
 

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Does anyone have any idea what a perfectly functioning battery temperature sensor (BTS) measures?

I can’t find anything online and I’d like to rule out the BTS as far as troubleshooting goes.

Here is what I measured:

51k Ohm @ 24 •F
16k Ohm @ 65 •F
10k Ohm @ 120 •F


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Does anyone have any idea what a perfectly functioning battery temperature sensor (BTS) measures?

I can’t find anything online and I’d like to rule out the BTS as far as troubleshooting goes.

Here is what I measured:

51k Ohm @ 24 •F
16k Ohm @ 65 •F
10k Ohm @ 120 •F


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i dont have numbers but that appears to be working ok. cold temps have the higher resistance values google coolant temperature or intake air temperatue chart for a rough comparison.
 

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Check the crossover wire from the left and right battery. I had a charging issue for years and threw a few batteries at it. Once I did some good research I found the cable had been corroding deep inside. This was causing recharging issues with the batteries. Just an idea.
 
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