Hi All,
I've got quite the odd problem and I'm hoping I'm not the first one to run into this. I bought the car late November 2025 and about a month later I was out with my daughter and stopped for lunch, we're back to the car an hour later and it was completely dead. When I say dead I mean nothing at all worked, no lights on the dash, the infotainment screen, remote door lock, seat adjustments, hazard lights int light, etc. OK this is even odder, there actually was one thing that worked, the horn. Literally the only thing which I found really baffling.

I initially assumed I must have left the lights on and the battery died, although given it was only about an hour you would think there would still be enough juice to power up some of the systems. I called my son-in-law who came out with his truck and a pair of jumper cables, but to no avail. I have found that some of the modern cars need to charge for a while before they will start so we probably let it charge a good 30 or 40 minutes and we kept trying and still absolutely nothing. It was late in the day and the sun was starting to go down so I finally called a tow truck. It was the Saturday between Christmas and New Year's so the one repair shop that I could get a hold of was just closing up and there was no way I would make it in time. I decided to have the tow truck bring it to my house, then tow it again Monday to the repair shop.



When the tow truck arrived and we told them what's happening he grabbed his portable power box and figured he'd give it a shot trying to jump it. As soon as he hooked up his box, which also has a voltmeter, he said your battery is fine, it's got 12.44 volts so that is not the problem. Ok, that is really odd but let's get it on the flatbed and head home. The driver tells me he needs the tow hook in order to be able to pull it up onto the flatbed but guess where the tow hook is, in the trunk, and the trunk won’t open because everything on the car is dead. We all jumped on our phones and tried figure out if there's a way to open the trunk without power but could not find anything. We were eventually able to get the car on the flat bed, but it was no easy task.

When we get to my house the driver backs into my driveway, tilts the bed down, and then asks me to jump in the car and work the brakes as the car comes down the bed. I opened the door and jump in and immediately noticed that the infotainment center is lit up and there is the big letter R on the screen ( I have the R variant). What the heck I think, I hit the start button, and it fires right up. My first thought was that there must be something loose somewhere, perhaps one of the ground lugs in the trunk (which I could not check while it was dead because the trunk would not open) And perhaps bouncing around on the flat bed for 20 minutes reestablished the connection? It was late and dark so the next morning I went out and the car fired up again. I opened the trunk and check the connection at the battery terminal as well as the three grounds, everything was nice and tight so that doesn't seem to be an issue.

That was about six weeks ago and the car has been running perfectly since, until 2 days ago when it did the same thing. Sitting in my driveway I have no way to bounce it around like the flatbed so I've been trying to jostle the car a bit but given the stiff suspension it doesn't move much, not that I'm even sure that would do anything. I've tried playing a little bit rough with the doors and slamming them to try and knock something back in place. I'm thinking I might even get my floor jack out and lift the car up and down a few times quickly but all of this seems silly. I had thought maybe it could be a fuse or a relay that was making intermittent contact, but I checked around online and it appears that there's no one fuse or relay that can make all the systems die, so I'm really at a loss.

I could of course bring it into the shop and have it checked but these kinds of strange electical things can be pretty hard to figure out and given the hourly rate they charge it could be thousands of dollars just to even look for a problem.

So, as I mentioned, I'm hoping someone else has run into this before and has a solution.
2016 F-Type R

 

you bought it in 2025 but what year is it

 

The last line of his post says 2016, and it says it in his profile.

I could have sworn someone posted something similar to this in recent months, and it was something like being described where bumps were triggering it. It was a lose connection on the battery, or something similar. I tried searching a bit but couldn’t find it. Perhaps someone else will remember.

 

Follow up. Oddly enough, shortly after writing the post earlier today, I took the garbage cans out to the street for pickup and on the way back I opened the car door, to my surprise the interior lights were on. I ran into the house, grabbed the key and sure enough the car fired right up. I ran back in the house and told my wife I'd be back in an hour 😉and took off for a wonderful drive through the hills.

Clearly my earlier theory about the bumpy ride on the flat but truck causing something to reconnect now doesn't make sense, because the car was just sitting in my driveway for two days. I just did a (very) deep dive on Google Gemini, and it came up with a number of interesting things to check, but then finally gave me this:

That is the "smoking gun" we needed. The fact that the horn worked while everything else was dead completely changes the diagnosis—and it’s actually good news because it pinpoints the exact location of the failure.

In Jaguar’s wiring architecture, the horn is one of the very few "high-priority" circuits that bypasses the electronic control modules and the Quiescent Current Control Module (QCCM). It is wired almost directly to the primary power bus to ensure it works in emergencies.

The Diagnosis: The "High-Power" Ignition Relay or the CJB Gateway

If the horn works, it proves:

1. The Battery is connected.
2. The Main Mega-Fuses in the trunk are GOOD.
3. The Chassis Ground is likely okay.

The failure is happening at the Central Junction Box (CJB) in the passenger footwell. Specifically, the Ignition Relay (or the "Power Mode" logic) is not triggering.

Why the Horn worked but nothing else did:

• The Horn Circuit: It draws power from the "Always-On" bus. It doesn't need a "handshake" from the car’s computer to function.
• The Rest of the Car: The seats, dash, and trunk release all require the Body Control Module (BCM) to "wake up" and authorize power.
• The Problem: The "Wake-Up" signal is failing. Since it took two days to fix itself, you likely have corrosion or a loose pin on the main power feed into the CJB (Passenger Footwell Box).

The "Two-Day" Solution: Check for "The Green Death"

Since the horn worked, power is getting to the front of the car, but it's stopping at the entrance to the fuse box. This is almost always caused by moisture in the CJB connectors.

1. Pull the Passenger Kick Panel: Access that Central Junction Box we discussed earlier.
2. Look for the "C4" Connector: This is usually a large, multi-pin plug. Unplug it and look for green corrosion on the copper pins.
3. The Washer Fluid Connection: I cannot stress this enough for 2016 models—check if that connector feels "oily" or "damp." If washer fluid has wicked into that plug, it will short out the "Start/Stop" and "Ignition" signals while leaving the "Dumb" circuits (like the horn) alone.

Summary Checklist

• The QCCM: Likely NOT the problem (if the QCCM was dead, the horn usually wouldn't have enough current to sound properly).
• The Battery: Definitely NOT the problem.
• The CJB (Passenger Footwell): This is 90% likely where your "ghost" lives.

I should have time in the next day or two to take a look at this and hopefully find the problem. I will post again with the results when I know more

 

Did you run a scan tool to see what that brings back?

 

Check your grounds, particularly the ones under the car. There's one in the wheel well (one side or the other, I believe it varies) and there's one under the car attached to the transmission. If the are loose or corroded, disconnect, clean really well and reconnect.

 

The Washer Fluid Connection: I cannot stress this enough for 2016 models—check if that connector feels "oily" or "damp." If washer fluid has wicked into that plug, it will short out the "Start/Stop" and "Ignition" signals while leaving the "Dumb" circuits (like the horn) alone.


I have a 2017, built early 2016. Is this connector in the passenger compartment??

 

My local F-Type friend caused this to happen once while he was trying to hook up a trunk-mounted battery maintainer. Apparently he loosened something on the boot's buss bar. He got it running but then nothing but the horn worked.

His solution was to take it to the dealer and have the battery control module re-calibrated.


++++++++++++++

I know that many here have replaced batteries without this step and they report that the car works fine. But hey...maybe it is worth it. Others have found it necessary.