GM Factory Installed Hydronic Heater Information Wanted.


Active member
Just dug up a couple things. The first picture is from GM upfitters and is for 2008+ line routing which might be helpful.

The other is a picture of a labeled harness for a pre-2008 but I imagine it’s pretty similar. Next step is for me to a to figure out what needs power. Im not sure at this point what the CAN hi etc actually means. I can’t read the sprinter forum schematic. I guess I’ll have to sign up to get a higher resolution picture of their schematic



Engineer In Residence
can means canbus, digital communication. If you look at the d5s main plug under the cover, there should be a pin for analog on/off. However it may not work due to custom programming.


Active member
OK, so after gleaning forums with posts from 2006 and up, I have determined that this is basically impossible to hack into. No one has figured out GM's module. It seems crazy with a world full of smart people out there but that's what I found.

Basically from what I can see is there are two options. Buy a Mercedes brand D5WZ and swap it in place and hack it as the sprinter guys have figured out(this does not work for the GM ones). The other option, which I'm leaning to, is finding an Espar Controller for an older D5WZ (I can only find "H" model controllers on eBay and amazon. So if anyone has a lead on how to find this I would appreciate it) .

If you go either one of these ways you will need to plug p/n 25828205 ( ) into the vehicle side of the FOH harness or your van will not operate correctly. This is how factory GM vehicles that do not have the FOH do it.

Either way, if you do either of these two options, you will no longer have an automatic mode. You will need to manually run the heater. Also, I haven't confirmed this, but I believe the Espar controller will only let you run it for an hour at a time so the Sprinter option may be better depending on what you are trying to do.

I'll add more if I find anything else out.