2006 charging at 15.8V

[zakkb787]

Hey guys. So this truck has actually done this since I got it. It’s a factory dual alternator truck, no intake heater anymore, and currently has two new batteries in it, though it was the exact same with the old Dekas I’ve had since I got the truck 4.5 years ago. Measured with a multimeter going into my amplifier directly from the battery, this thing charges at 15.7-15.8 volts pretty frequently. Usually within the first 30 minutes of starting (cold or hot). Hot weather, cold weather, it’s always done this. I’ve had the entire charging system checked at a shop and they found no issues with the alternators or regulators. It was never really a problem until this weekend when I installed an aftermarket head unit and 5 channel amp. Once the amp sees 15.7v it’s going into protection mode till the truck chills out at 14.4 ish volts. So my question is first, why is this thing charging so high? I scoured all the forums and everyone said oh 15.3 is normal for these, but never saw 15.8. Second, if there is a problem, where in the world do I start?

 

[Chevy1925]

These are ECM controlled iirc. before you crank the thing up, whats your resting battery voltage? it may be a parameter in the ecm that tells it to overcharge the batteries some to bring them back up to snuff quickly.

can you pogram the amp to change its protection mode?

 

[2004LB7]

15.8 does seem a bit high even for the equalizing or boost charging. As James said, the ECM controls the duty cycle of the alternator regulator. Maybe the 12v supply to the ECM that it uses to monitor the voltage has corrosion or something else that is causing excessive voltage drop and the ECM is trying to bump it up until it comes to it's expected level. If you put a scan tool on it to read out the voltage the ECM sees does it match the multimeter?

 

[zakkb787]

Unfortunately the amp isn’t adjustable. Crutchfield is sending another one just in case (Infinity 7005A) but I’d guess the issue will still be there. So, after sitting for a couple hours last night when I initially plugged up the multimeter with the key off it was somewhere between 13.5-13.7 volts. Which in my mind should not warrant for this much of a charge. At idle, in seeing 14.4v which is the standard. Any sort of RPM and it jumps to 15.3-15.4. I just drove it to town and saw 16.04v sustained. The ECM is reading within 0.1v of what my meter is reading. Tomorrow morning I’ll read what it says after sitting overnight

 

[Chevy1925]

Your batteries shouldn’t be 13.5 sustain after sitting, key off. They should be around 12.6. Now they will show 13.5-13.7 after the alternator charges them but they should slowly drop to the mid 12’s

 

[zakkb787]

Your batteries shouldn’t be 13.5 sustain after sitting, key off. They should be around 12.6. Now they will show 13.5-13.7 after the alternator charges them but they should slowly drop to the mid 12’s

This was only about an hour of sitting. I’ll check it in the morning for a more accurate reading

 

[Chevy1925]

Did your truck come factory with dual alts?

 

[2004LB7]

Can you try unplugging the connector on one alternator at a time and see if it stops?

 

[zakkb787]

As far as I know yes, but I don’t have the actual build sheet. If it’s not, they took time to make it look 100% factory. I’ll try unplugging it next time I leave

 

[Chevy1925]

Look for KHB in the glove box where the RPO codes are listed.

 

[tractor]

A bad battery can cause this also.

 

[2004LB7]

A bad battery can cause this also.

Very possible but it sounds like the issue was present before and after the new batteries

 

[zakkb787]

Okay so battery voltage after sitting overnight is 12.86v. Unplugging the second alternator plug did not help, still seem to be getting well over 15v. This was even just sitting at high idle. I do not have KHB listed in my RPO codes. Closest thing I have is KNP and KUP.

A few interesting points. With the second alt unplugged (just the 4 pin plug), the system still functions and I’m getting well over 15v. If I plug the second alt in and disconnect the plug on the first, it is still charging at 14.4v but I’m getting a battery light and battery not charging message. Now, would this indicate that my tune is set up for only a single alt? I have a single EFI tune from a member here. Also, could this mean the factory alternator on the original location could be bad?

Also should note that when I had my system tested, it was not a bench test. They plugged some fancy machine onto the battery or alternator or something and said it was all good to go.

 

[2004LB7]

Makes me wonder where the 2nd alternator was wired in to. And if the 1st alternator regulator is bad. I'd pull it and have it bench tested. Or maybe swap the two and keep the 2nd unplugged and see if it holds

 

[zakkb787]

Makes me wonder where the 2nd alternator was wired in to. And if the 1st alternator regulator is bad. I'd pull it and have it bench tested. Or maybe swap the two and keep the 2nd unplugged and see if it holds

Kinda long these lines, I’ve been thinking of how to isolate whether it’s a possible tuning/wiring issue, or a bad alternator possibly. So my remedy for this currently is to unplug the factor alternator. Now this does give,e a battery light and vehicle not charging warning, but it does actually charge. Runs at about 14.6v unless I turn the music up then it drops to 14 ish or lower when I’m idling.

A question for the tuning guys out there, is there a difference in the tune of a single and dual alternator truck? If so, maybe my tune is for singles and is causing some kinda weird issue?

So, given all this, could I not swap the alternators and unplug the second one and see if the problem persists? If it does, this leads me to believe tuning issue, because if the truck charges normally with the second plugged in, so I know (in theory) that the second alternator is good since the max I saw out of it was 14.6v when it seemingly wasn’t being controlled by the ECM. Now if it does fix the issue, I’ll know that I have had a bad alternator.

 

[2004LB7]

I don't believe the tunes are different. I believe you can just plug in the wire to the correct pin on the ECM and it works with nothing else to do

If you can, swapping the alternators and doing the unplug test should reveal if it is one of the alternators

 

[zakkb787]

I come bearing possible good news. Swapped the alternators, left the second one (that was originally in the factory spot) unplugged, and voltage is the correct 14.4 ish. Granted, this was while the truck was already warm and a very short drive, but tomorrow morning will be the real test. As of now it’s looking like I just need an alternator. I’m assuming I need to get the factory 105 amp for dual alts? Or does it matter what size I get? I don’t want to overload the factory wires.

This brings me to another point to note, the second alternator power wire is wired into the factory red box on the driver side of the engine, and the harness is wired into the factory harness. If it’s not a factory job, someone sure took time to make it look that way.

ALSO, completely unrelated, but I found my coolant leak finally. Anyone have the part number for the o ring for the metal pipe that goes into the top of the thermostat housing? I’ve had to buy one before, but I can’t remember the number because I ended up having to go to the dealer after mine got shredded.

 

[2004LB7]

That's good to hear. I would do the 145 amp alternator. As long as the output wire is of appropriate size I wouldn't worry about overloading it

For the o ring, are you looking for item #23 in this picture? If so it should be 94011604

 

[zakkb787]

The wires going to the alternator look quite small, I’ll price out what each alternator will be and go from there. Might get a slight upgrade if it’s around the same price.

I think the part number I’m looking for is 94011605, it’s the o ring for the metal pipe with a 90° bend that plugs into the top of the thermostat housing, I believe it goes to the heater core maybe? Haven’t been in one in so long I can’t remember

 

[1FastBrick]

The K code shows the alt size. I think KG3 is the 145 amp. To my Knowledge all the LBZ's had 145 amp unless it had a Dual alternator or maybe something else like a snow plow prep.

What I was reading online is that the dual alt set up used a 145 and a 220 amp set up? I wasn't able to find out a whole lot about the dual alt package though.