Hi all, I'm new to the forum so please be gentle!!! I'm looking for advice on the fuel heater. I have looked at the various posts on the forum.
Mine hasn't worked since I took ownership two years ago. I have replaced the battery with a new quality battery just for best practice and peace of mind. I'd like to try and resolve the fuel heater before winter. I've only done some very basic checks and have removed fuse 13 engine bay to allow a reset. There is battery voltage to and from the fuse. I located the ambient air sensor in the n/s/f mirror and would like to disconnect this to go into default -40. I've removed the mirror glass, see the sensor but no connector. Could someone kindly confirm it's behind the n/s/f door panel please?

Also, am I right in saying I could access the heater under the wheel arch and run a separate 12v feed just to see if the unit initiates for test purposes? Currently, the remote works and is coded but when pressed, the interior fans work for about 15 minutes then shut down. This was also the same in very cold weather. Any help from you guys is so very greatly appreciated and welcomed.

This is a well discussed topic on the forum and a frustration for many new owners as you have something useful on the car that refuses to work as it should. I have the same frustrations as you: my FBH is fully functional but will not run long enough to actually heat the cabin. In fact it has only ever done this once which was immediately after I installed a new AGM battery.

The best way to test the FBH is via the GAP IID tool as it allows override of the ambient temperature thresholds ( as I remember).

If you have doubts about the remote operation you can invoke the FBH from the infotainment system menu. There’s a way of doing this without having to set a timer but I can’t quite remember it off the top of my head.

TDV8 4.4 have an overly complicated battery management system ( IMHO ) which in the case of the FBH seems to work against the function of the vehicle. As I understand the BMS limits the maximum charge % of the battery so it rarely reaches maximum. The FBH controller switches off the FBH when the battery voltage falls to a certain level ( from memory I think this is 12.4V ). The net outcome is that these two systems seem to work against each other so the effect is that the battery rarely has enough “ooomph” to run the FBH for the full 20 minutes so the cabin never gets warm.

Some owners install secondary batteries in the boot with voltage sensing relays to give more ooomph. I’m not sure if this approach overcomes the FBH issues on the 4.4 or not.

I’m considering installing a dedicated 20 AH Li Battery to supply the FBH. I’m still thinking though where to safely mount it and the requirements for charging it independently of the BMS.

I hope this helps and I’d be interested to hear how your investigations develop….. good luck ! TDV8 4.4 2012

When I purchased my 2011 4.4 TDV8, mine also hadn't functioned for several years, however the previous owner thankfully told me the issue so I could sort it.

The issue was a corroded and seized fuel pump for the FBH. If the FBH doesn't detect a fuel feed, it won't run.

It was quite easy to check - put the suspension up and get a camera or phone on a selfie stick to look up between the rear diff and exhaust. The pump is directly above. If looking yourself, please position axle stands under the vehicle and leave the driver's door ajar before heading beneath.

Click image to enlarge

@GaryRR: great tip. An additional check is that you can hear the pump ticking from within the cabin when it is working. I can hear mine within a few mins of starting the car on cold days regardless of if the cabin heater has been set on or not. I think this is to do with getting the engine heating up to temperature more quickly in cold conditions. TDV8 4.4 2012

Might want to try this "bridging" as a check



 Gone to a good home: 2011 4.4 TDV8 Vogue SE Buckingham Blue with Ivory and clear glass = "Rory"
2025MY Defender D350 90 in Silicon Silver on coils
1974 Series 3 Lightweight = "Millie"
Many, many other Landies over the years
My preferred specialist: www.glenrands.co.uk
--------------------------------------------------

Thanks to all who replied. I'll let you know how I progress with this, I don't have the IID tool I'm afraid hence me trying to disconnect the air sensor into default mode. As soon as I get time, I will have a look in the wheel arch and see what I can find.
I can confirm that the heater doesn't even attempt to start or make a noise. There is no initialisation at all other than the interior fan blowing.

I'll keep you updated and truly appreciate your feedback,. Thanks

Could be the small coolant pump that is bolted to the actual FBH itself.
The IID would show this straight away. Go buy one  Gone to a good home: 2011 4.4 TDV8 Vogue SE Buckingham Blue with Ivory and clear glass = "Rory"
2025MY Defender D350 90 in Silicon Silver on coils
1974 Series 3 Lightweight = "Millie"
Many, many other Landies over the years
My preferred specialist: www.glenrands.co.uk
--------------------------------------------------