Battery Over Chrage

[Ghosty]

Hi All,
I am chasing some info on how to reduce the charge rate of the Alternator on the 6.6 Dmax LMM units. (Alternator is Brand new) Has 2 light gauge wires into harness, one HD to battery

I have just done a trip of 4000+km's and popped two batteries on the trip from over charging. One was the original, the second a brand new battery from a vendor along the way.

The Alternator is putting out 15VDC all the time even when fully loaded it only drops to 14.8vdc
This high charge rate combined with under bonnet temps of 100Deg C is frying my batteries.:mad:

I have heard I can change the charge rate in the ECU, is this correct. Can anyone point me in the right direction to do this. I have an Edge CTS to use as a coms tool. Happy to be told what else to buy if this is not good enough.

Thanks in advance.

[DmaxMaverick]

The charge rate can be reprogrammed in the PCM, but you'll need a Tech II tool, and a technician who knows how to do it. The process isn't "standard" GM issue, but can be done with a savvy tech. Other than that, you can check if a later calibration is available, and what it addresses. Any dealership service department can check with only your VIN number.

Also, having 2 miss-matched batteries may also kill them. Miss-matched by one new and one old (failing), different brands, or significantly different capacities. Batteries should always be considered a matched-pair. Once they are about a year old, they won't "match", even if you replace with the same brand and capacity. The subtle imbalance between them will often kill both.

[Ghosty]

Hi DmaxMaverick,

Thanks for the reply, this kit has been retro fitted to a Nissan Patrol, in Australia, so no dealers, let alone one who would know where to look.

I will chase down a Tech2 tool and see what I can find on forums for the codes to change.

You have at least confirmed that I can do it and what tool I need so this is a great start.

Thanks heaps

[DmaxMaverick]

Sounds like a nice conversion.

As far as it goes with a dealer, nearly any of them can do it, but if you have a GM dealer, that would be better. It doesn't matter what vehicle it is in, it should still have a Duramax PCM, and OBD-II diagnostic port. You only need to find a tech who knows his/her way around inside. The Tech II, or compatible other tools (Rotundo, Snap-On, etc.), are nearly universal with OBD-II. Changing preset values should be simple, with any of the compatible tools. Many independent shops have the same ability, too. Check around.

[Kennedy]

I would first ask for a definition of "brand new" alternator? Is it GM or off brand?

Like Mav stated, start with a pair of matched batteries.

This is not an issue that is common with the Dmax by any means. They do run a pretty high operating voltage though when a battery needs charging.

[Ghosty]

HI All,
Back on this problem again, I bought a 13.8vdc reg from a place in the States. replaced the reg i the Alternator.
Same thing 15Vdc output yet again.
Spoke to the Alternator guy in the states and he says that reg / alternator voltage is determined by the PCM (assume he means ECM in DMAX)
Looked up the drawings, and the e;ectrical drawing shows a pull down switch (variable) and a bridging switch on the same output to the field. SO this aligns with what the alternator guy says.
Does any one know where to set this voltage using a Tech 2? I can see the voltage as an Info filed but don't know where to adjust it. I have only had my Tech 2 for a day, so I am unsure where I should be looking.

Thanks in advance

Ghost

[Ghosty]

Hi Whats the chances there are two different model ECM's or programs where the cold temp Alternator charge is 15vdc, and the high temp is 13.8vdc?

Also I dont have a battery temp monitor, or a charge current monitor, is this going to matter?

Thanks
Ghost