How to prevent ignition from auto shut off ?
 

There has to be a simple solution to keep ignition from auto shut off every 10min or so , maybe some kind of service mode to prevent this ? I can't find it. 2013 XJ
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No there is not because XJ, like many modern car, consumpts something between 10-20A when ignition are On and engine not running.
Each shock alone 0.5 - 1.5A (multible by 4), injectrors are high fregrency / high pressure types (8 of them), multible computers, dual screens with high brightness etc, etc.. The battery will drain quite fast if you leave ignition On for long period.
Only method i have seen ign stays on for long period are during SDD session, but then external battery feeder should be connected anyway. (20A-30A)

But there are) At least two ways, both of these are used to program the modules. For example one of the buttons on a screenshot below - turns the ignition to on (even if there's no keys in car), without an allowance to start an engine. And the igition status can be maintained for days and hours if there's enough power supply.
Actually there's even a way to prevent a car/module from going to sleep while flashing.
https://cimg1.ibsrv.net/gimg/www.jag...411cd5d232.png

Exsactly: On diagnostic tool usage only.
The systems wake up when you plug diagnostic tool on OBD port even ignition are Off. You can read VIN code etc, so if you have 3rd party telematics or HUD displays connected to ODB port you can drain the battery fast, since the car don´t enter sleep mode.

Not exactly. If a diag tool is using only generic UDS or OBDII requests, not broadcasting a wake-up or TP signal the CAN-buses would go to sleep mode. Since that there'll be no comms, the only additional current draw would be to keep a power on a diag tool (the OBDII power is not switched one), however it won't be quite high.

There's still a way to keep the ignition on for a prolonged periods of time without any kind of diag tools :) It was in one old enough TSB in Topix (IIRC this TSB is deleted now).

I Figured there is a way to do it. So what's the procedure to stay ON without any dignostics tools connected ?

Never seen one diag tool not broadcasting, have you?

Not a lot of the tools are broadcasting a TP or wakeup for diagnostic purposes, there's just no point in that.
Other broadcasts are ignored once the module/network decided to go to sleep mode.
Even if TP/wakeup are present, even if tester is broadcasting it - there's a timeout hardcoded in bcm and/or gwm (actually two - for locked and unlocked vehicles), which would render a can to sleep once the timeout is met and ignition is off.
There was a lot of cases, when one module won't go to sleep due to the bugs in a software, and if you'll dump a can data it's pretty clear that the other ones are still sleeping.
So the only issue with non-unplugged diagnostics - is the current draw to feed the device itself, not the whole network. Been there a lot of times :)

P.S. In a JLR there's a whole lot of modules that are NOT liking a TP/broadcast, not happy with these signals and behaving abnormally if these are present ;)

Correct, hardly ever seen diagnostic tool with TP / wakeup, but seen only one what did not broadcast. It was loooong time ago, at -90:s when firsts OBDII ports appeared. It was just reading. As long as there are brodcasting, the CAN stays awake even Ignition be turned off. Most of the systems will shut down but as you seen as well, not all modules like that and stay awake. Easy to read CAN stream with just inductive CAN reader.
It´s not only JLR. Seen same in other margues as well. Typically owners have telematics devices on OBD port what are capable to read and sent data from car to their phone, for exsample Gas, Range, Temp etc... without them realising that the device have to keep systems up and running to read the data -> And then battery are drained .. :icon_bricks:

Let's get an SDD as an example. During initial scan it uses the broadcast UDS requests to collect some data from modules (basically to check what modules are present), then it collects a data from every present module directly. Then, if you'll leave SDD running and connected, ignition off, the can buses would go to sleep and the drain would be normal drain+j2534 adapter drain, nothing more nothing less. Even if you'll try to connect to some modules on a can bus (not touching door locks/etc) - there would be comms error and no increase of a current drain (checked it quite a few times). Same with DoIP/Flex vehicles.
Even on a bench, once the module (BCM/GWM present) goes to sleep - no comms. The only way to prevent it from a sleep is constantly send a UDS requests (not a regular CAN messages, but UDS ones), but it's rare for telematics/whatever to send a UDS requests constantly, there's hadrly a reason for it.

Weird, there might be differences, since mine (+2 other brand vehicles) left for an hour with SDD connected (and other vehicles diag tools) and CAN was still alive and kicking after that.
Thats what these telematics OBDII dongles are made to do. Otherwise there are no sense of them.

There's some more variables. Locked car gets to sleep in 15min, unlocked may still have some occasional comms for a few hours. Then it's if the key is near/inside or not - makes sense too. Best check is to "lock" the vehicle, get the keys out of range and that's all. Very minor draw.

Sure, i am familar about unlocked / sleep modes. Very simple test: Leave diagnostic tool running with CAN analysator aside of it inside, so you can see it thru window, lock the vehicle and take the key away -> After one hour CAN is still alive. Do same without SDD connected and CAN is flat in 10min. There are also differences if you "double lock" it, but i made tests with single lock. Other marguee (german) did actually went sleep much much faster (less than 2min after locking), but i noted that it did sent some data thru CAN every 20min. it is much newer gen system with onboard telematics, and i think it is the status & geoposition update for the cloud service. The 20min interwall would suite for it.

This is far from original thread, interesting, but non useable information, exept fellows who are keen to know how things work. Original question was gan you have ignition On for longer period: Yes, but need extra equipment, not possible with just a car like it is.