New here too and am hoping to find a solution to this terrible feature as well. It should at least default to the disabled state. I personally don't like the feature for the following reasons:
1) Each time you turn off the engine, the internal temperatures spike up.
2) Each time you turn off the engine, the oil pressure is lost.
3) Finally, and it is a long stretch, but starters do fail. I would rather it fail in my garage when I first start the car than when I am sitting in stopped bumper to bumper traffic on the freeway.


I personally don't believe that it saves any significant fuel and it is more of a marketing gimmick than anything.


Is the second battery installed just for this feature? I don't even know if my 2015 has one? Thanks if anyone comes up with something.

 

How I did it for a 2016 XJ...
Remove the trunk floor exposing the battery, spare, etc.
At the back end (towards front of car) of the battery is a thin, rectangular, silver module attached to a bracket. Several wired plugs are attached to the face of this module. The small black plug closest to you, with the SMALL GAUGE colored wires, can be unplugged. Secure this disconnected plug.
When you start the car, after about 30 secs., the "ECO OFF" light will illuminate in your dash.
No more stop/start, and no problems for me so far! Let me know if this works for you too, or if you notice any other issues...
Good luck!

 

THAT'S how you do it!!






According to my dealer, it's not a battery, rather a capacitor. Either way, yes your car has one, and that's what it's for............and it's also the "thingy-mabob" that you disconnect, to defeat the inconvenient as hell, eco-start.

 

Works perfectly! Thank you!!!

 

I did the unplug on my 2016 XJL and it did disable the start stop feature but I also think it disabled the horn beep when locking the car. Not positive about this but tried it several times and the beep did not happen.

 

Now ... if it also stopped the irritating horn beep when you get out of the car and close the drivers door with the engine running (even in Park and the e-brake on) ... then it would be worth disconnecting even betterer!

 

The second battery is switched in when the s/s activates to supply sensitive modules with a stable voltage to protect them from glitches incase the main battery drops its voltage. This leaves the main battery to supply the tandem solenoid starter for the restart.

 

That's interesting.
Why would that apply only to cars for the start/stop function? Wouldn't that be just as much of a concern with any car when it's started?

 

Actually the small battery is used to avoid drawing down the big starting battery while you waiting at a stop light. Jaguar did not want the SS stuff to cause your car to NOT re-start when you touch the gas pedal.

That's also why when there is any kind of failure the SS is shut off and the system reverts to the normal one battery setup. It's to protect the starting battery if possible.
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Yes Mark, low voltage for non s/s cars has always been an issue. My previous 4.2L v8 X350 would throw all sorts of fault codes and warning messages if the battery was low on volts. Think even late non s/s X351 suffer similarly. I always disable the eco (laugh) mode on every start, prefer to have a fully charged main battery. I also now have a bluetooth battery monitor fitted across the main battery so I can monitor the state of charge.

 

My ultimate solution to disabling the stop/start feature was to disconnect the ground lead on the small battery on my 2014 XJ. However, at the time, I was still on CPO warrantee and I worried about that disconnect being detected when taking it to the dealership and having them plug in for diagnosis so I put a motorcycle battery switch in line with the small battery ground lead. That way I could easily switch on the small battery. Prior to that, I toyed with the idea of trying to fake out the system by causing a false inhibit since there are many things that inhibit the stop/start from coming on. I didn't follow through with that thought fearing unintended consequences. The list is big as follows:

Auto Stop/Start System Inhibits

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  • Auto stop/start off switch has been operated by driver
  • Transmission not in neutral
  • Hood open detected
  • Driver door detected open
  • Driver seatbelt not fastened
  • All terrain progress control special programme selected
  • Climate control demand exceeds calibrated threshold
  • Heated windshield operating
  • Trailer connected
  • Brake booster vacuum below threshold
  • Engine coolant temperature below threshold
  • Engine oil temperature below threshold
  • Battery state of charge low
  • Battery cold cranking capability below threshold
  • Ambient temperature above 40°C
  • Ambient temperature below 0 degree C

 

I own a 2019 XJL. On short trips I want it off, on longer trips or those with lots of stop signs/lights I want it on.

 

Seems like you would just use the eco switch for this type of use. For permanent off you would unplug the smaller wire group from the capacitor located in the trunk.

 

On some US light trucks, certain nusiance features are also disabled when a trailer is attached to the vehicle. A friend inhibits his Chevrolet truck performing the multiple cylinder deactivation feature with a small passive device that plugs into the trailer lighting connector, mimicking an attached trailer.
Maybe an elegant solution to performing this modification to the XJ is possible. The car would behave normally; no stop-start warning light, etc.

 

What's funny is Jaguar specifically forbids any trailer usage on the X351!





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Actually that makes perfect sense to me...
What's funny to me would be considering an XJ for towing duties!
I'm assuming Bernie was suggesting in fewer words (assuming that other forum readers share his & your common sense) that a (reasonably & relatively) simple modification to the wiring that would seamlessly disable the start/stop feature that's elegant in it's simplicity. Of course as complicated as the lighting system is, the example that Bernie provided wouldn't work with the Jag XJ - it's a way to use the design features in, say the XJ's sibling the Range Rover, to disable the feature. If there is any extra load or deviation from the designed load/current draw on any light circuit in the XJ (and the Range Rover as well), the vehicle will detect it and throw a fault. And as you point out, the XJ is never... ever... to be used for towing... anything... ever.
I may be wrong, but I think Bernie presents the challenge for readers to use our own grey matter & resources to look for elegantly simple ways to use the XJs own design to find answers to the question.

 

The challenge you suggest was my thinking when I posted that stop/start inhibit list. It seemed apparent to me that the list came from the Land Rover side of JLR with that trailer inhibit. It looked like an attractive entry point to fool the system but not having any assurance that the XJ had a trailer output even considered in its design left me on the cautious side and I sure didn't want to mess up a perfectly functioning system with any experimenting i.e. unintended consequences. So, I put up with the no stop start warning light resulting from the disconnected ground lead.
Another thought and direction: There is a guy, Steve Klonsky, who has been making and selling devices that plug into the SDD port for GM and Chrysler vehicles that disables the stop/start feature. (Smart Stop Start - HOME) I've tried to get his attention to focus on developing a device for us Jaguar customers since 2018. He has replied to me that he might consider it for the future. Maybe more of us could encourage him to develop a fix. I'm sure his market and customer base size isn't with us guys, though.

 

Yeah, I've seen those too; a dongle that plugs into the OBD port. I shoulda been suspicious of your "Inhibits" list, as it includes a provision for off-road conditions (something else not reccomended on an XJ )

 

Please; I'm getting horrible visions of XJ's fitted with outsized suspensions and big mudder tires, or a hooptie XJ with a towing hitch pulling a small flatbed trailer with a lawn tractor.

As an outsider (someone who's 2012 XJ doesn't have the stop-start feature), ideas being discussed to answer the challenge make me think of maybe a jumper to trick "the system" into "thinking" there is no aux battery installed when really there is. As a casual observer of what posts by those with the feature have described, it sounds like that would work for those that would prefer to not just disconnect/remove that additional battery instead. I may be wrong, but as I understand, that's the only purpose of that extra battery, and when it's disconnected/removed, the start/stop function is disabled.

 

There's a button on the dashboard to defeat (and restart) the Stop-Start system, but you have to push it every time you start the car as it automatically resets when you shut off the engine.

Is that too hard for you to do?