C-MAX Energi Auxiliary Heater Core: Bypass / Disable or Replacement

[vballvic]

I have a 2017 C-MAX Energi. Recently I discovered a coolant leak which I have tracked down to what appears to be the auxiliary heater core.  It's a black box located in front of the passenger wheel well with radiator hoses and an orange high-voltage cable leading to it.  Unfortunately the leak appears to be coming from the middle of the housing and NOT from the hose connections. I don't see an easy way to fix the leak. I looked into buying a replacement part but the heater core (part # FV6Z18K463E) is about $600-700 shipped. Being that I never use the heater when in EV mode and the heat is generated by the engine when in hybrid mode, I'm thinking of removing the aux heater core and bypassing the coolant circuit with some radiator hoses and connector/clamps.

 

Anybody have any experience with removing or at least replacing the heater core? It looks like it can be accessed by removing the wheel well liner / inner fender. I can't find any online tutorials or videos on this particular repair / topic.

 

Some foreseeable issues are:

1. Risks of handling the high voltage cable: The cable is connected to the rest of the system via a harness clip near the coolant reservoir and should be easy enough to simply disconnect. I think it should be safe to assume that there is no power when the heater is off, especially with the car off. Even if there is voltage, I think it should be safe enough to unclip the cable and cap off the live-end with some electrical tape.
2. The system might see the heater core missing and might throw some trouble codes. I guess the question is how badly do you think the vehicle will react to this? Will it disable the high voltage system completely making the car undrivable? Will it just throw an error code notifying the driver of the "issue"? Or will it go unnoticed until someone attempts to use the heater in EV mode?
3. Is there a fuse to pull to disable the system from trying to activate the aux heater core?

 

Any suggestions or feedback welcome.

 

Edited February 18, 2022 by vballvic

[cr08]

A couple of notes:

 

1) I definitely wouldn't recommend using plain old electrical tape and even so I'd avoid messing with this at all if you aren't completely comfortable messing the HV systems. Proper isolation of an open connector HV like this would need to be done and is at least well outside of my wheelhouse. Wouldn't be difficult to have an HV connector in the elements, improperly isolated, and have it arc over to the body and wreak all kinds of havoc. There are some safeties involved, but those usually mean the vehicle will completely disable the HV system and thus the vehicle altogether once it senses there's any form of crossover.

2) Couldn't tell you how the vehicle reacts with it removed. Will very likely set a number of codes and could potentially cause the ICE to run 100% if it is unhappy enough. I -CAN- tell you that even though you drive in hybrid mode while using heat, it will still use the electric/PTC heater at points as needed and the vehicle likely takes this operation into consideration for emissions (making sure the engine can warm up in a timely manner, per their own OBD operations document).

3) There is a fuse in the under-hood fuse box labelled F29 but it controls both the A/C compressor as well as the PTC heater.

 

I'd verify that you are CERTAIN this is where it is leaking from. Clean it up good and check where it's coming from. Make sure it's not a hose or clamp or something nearby. Tighten things up if you can, etc.. I believe the degas/coolant bottle is also above this area as well as the washer fluid bottle. IF the PTC heater module is leaking, then that's about where I'd end my advice given it is a HV component and safety concerns are involved there. Absolute BARE minimum, pull the HV battery disconnect that's behind the rear seat on the passenger side. This essentially splits the pack in half electrically and opens the circuit. But there's a LOT more safety precautions normally involved beyond this step. High voltage equipment is no joke, especially DC.

 

You can also review Ford's OBD operations document linked below. Starting on Page 104 it covers the cooling system in detail.

 

Microsoft Word - OBDSM1700_HEV.docx (fordservicecontent.com)

Edited February 18, 2022 by cr08

[cmax2016]

Any updates on this ?

Edited October 25, 2022 by cmax2016
Duplicate

[cmax2016]

Any updates on this issue?

[Todd]

Hey I just realized I have the same problem. Did you ever figure this out? I'm debating pulling it apart and trying to reseal it. 

 

Update:

 

I took mine apart today after disconnecting the high voltage. It's a two piece body that comes apart rather easily by pulling the clamps off. I then used black silicone over the original rubber seal. 

 

Edited February 26, 2023 by Todd
Update

[WMark]

Just discovered I have exactly the same issue. There is a slow leak coming from the PTU. I’m debating having my mechanic attempt to stop the leak. I noticed that it’s been a year since Todd posted his comment and I’m wondering if the problem is fixed.