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Thread: Fuel tank sensor glitch

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    Junior Member sclayman's Avatar
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    Fuel tank sensor glitch

    Here's a wierd one.

    Yesterday I filled her up, and after about 20 miles of driving I got a warning message: Fuel Low.
    I was thinking that was very strange, and as I was driving along I watched the fuel tank pointer drop from full to empty, over about 1 1/2 -> 2 seconds.
    It didn't jump down in one step, there was a nice animated graphic

    At that point, I also noticed that the amount of distance remaining estimator didn't say zero but had ---

    My wife wondered if there was a fuel leak. So I stopped the car, had a look underneath, and there were no signs of fuel leaking.
    I restarted and all was fine.

    I've seen this afternoon on the XF forum there are some wierdies in this area.

    So have any of you seen this strange behaviour.
    2016 X351 XJ 3.0D

  2. #2
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    the fact the range read --- (error) means most likely the level signal was implausible. The gauge will be very heavily damped, hence the slowness in dropping.
    2010 XJ Portfolio running on lorry fuel. I know, Jag Diesel is just wrong!

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    Senior Member Cris's Avatar
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    A couple of times after filling the tank i’ve programmed the satnav to travel to work (170 miles) and the nav has said ‘insufficient fuel’ even though the range said 600+. Different to you but another weird example. All computers glitch and need restarting every now and again.
    2012 XJL Portfolio 3.0D - Premium Rear Comfort Pack, Driver's Pack, Illumination Pack.

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    Junior Member sclayman's Avatar
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    That restarting event, now and again , should in my opinion be measured in years ....... However, I think systems are getting worse, not better.
    I had a Linux box run for over 5 years non-stop, and only got rebooted when the building power went down.
    There are plenty of Sun servers that ran for over 15 years. I think the record for non-stop running is over 24 years.
    No current device will do that - the software is just rubbish. My Mac gets worse by the year, phones even worse than that.


    TheBoy observes that the fuel gauge sent an implausible value, it was possibly sending junk data for a while.
    It seems that such events were common enough during design and development, that the code for receiving this fuel gauge data
    has factored in these errors and presents this damped, slowly dropping display.
    So are we observing poor components, a harsh environment, or really good error handling.


    From what I can see, car electronics systems were always a bit of a mish-mash, and also cars have the benefit of getting a reboot for every journey.
    The forum discussion on JagDroid was interesting, and also illuminating as to how these car systems are put together in a rather erratic and un-systematic way, probably as a side-effect of the big bunch of existing parts they want to use up.
    I am not sure if our modern Jags are any better. I hope they are - there are so many components that are electronic. If someone knows, I am keen to find out.
    2016 X351 XJ 3.0D

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    Quote Originally Posted by sclayman View Post
    I had a Linux box run for over 5 years non-stop, and only got rebooted when the building power went down.
    There are plenty of Sun servers that ran for over 15 years. I think the record for non-stop running is over 24 years.
    So a quality patching regime was in place, NOT! That's even more scary

    Quote Originally Posted by sclayman View Post
    Quote Originally Posted by sclayman View Post
    No current device will do that - the software is just rubbish. My Mac gets worse by the year, phones even worse than that.
    Yes, most devices will. Windows will, Linux will, most Unix will. These general purpose systems are pretty robust as long as applications running on them behave (and in the case of Windows and Linux, sufficient resources are available). Even crApple products (bar the Mac, which is a bit crashy of late) - iPads and iPhones are supremely stable, partly by the software controls Apple enforce (on non jailbroken devices).
    2010 XJ Portfolio running on lorry fuel. I know, Jag Diesel is just wrong!

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    I had this happen once on an xf the gage was saying empty and the message was saying out of fuel I new there was plenty in the tank I took it to a dealers and they said can’t look at it for a week but it will be ok just keep it topped up drove it around for two days like this running ok on the third day it conked out and refused to start called Jaguar help line the AA turned up I explained what had happened he said I bet I know what that is, he laid under the rear of the car hit the fuel tank a couple of times with a rubber mallet and sure enough tank now saying full and car started ok, he plugged his computer in and cleared the fault, and said it will need a new fuel pump and fuel sensor as the sensor is attached to the pump, the car was under warranty the dealer didn’t want to replace the parts as in his words it was working ok now, I let the know exactly what I though of them they had the car in and replaced the parts or so they said never had any more trouble with it
    XJL

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    Senior Member mac_doctor's Avatar
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    Quote Originally Posted by sclayman View Post
    No current device will do that - the software is just rubbish.
    It isn't completely the software's fault: the problem is that everything is just too darn complicated.

    In the olden days, when I started as a programmer, computer programmes ran on a single processor, and mission critical stuff essentially ran on the bare metal. All programmes were deterministic (if you do this, that will always happen) and so it was actually possible (if tedious) to test every single possible path through the programme.

    Nowadays with multiple threads on multiple processors and multi tasking in multiple operating system modes - predictive processing and just in time everything: combined with no such thing as "bare metal" - all the processors are optimised to do certain things (which means that they actually contain programming): then it is a miracle that they do anything that they are expected to do. Testing is partial at best, as it is actually impossible to predict every possible path through the software. And that is just the easy bit.

    It also doesn't help that everything operates at essentially a molecular level, so electromagnetic interference can - and does - actually effect what the software does, and stray molecules can interfere with the micro electro-mechanical parts of the gizmos (see recently the news that a Helium leak in a hospital broke all of the iPhones on the premises, because the helium molecules got through the seals and stopped the system clocks - how do you make a seal that can keep out a helium molecule?). So even if the software thinks that it is doing the right thing external influences can interfere with the expected results.

    As I said - it is actually a miracle that these things work at all!

    (... and all of that applies to software created by people that are dedicated to the task, not car manufacturers for whom it is probably the 43rd most important thing in their day!)
    Chris. T.
    2000 XK8 4.0 Coupe
    2010 XJ SWB 3.0D Portfolio. With TVs. Lots of TVs.

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    Had exactly the same on my Merc S320. Twice, but have never seen it again ! On my reader it said 'Implausible message from sender--- so it is just the same. If I were you I would just forget it. Glyn

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    Trouble is if its a diesel, the car will shut down if it believes there is no fuel. As per the glovebox manual. So it cant be ignored.
    2010 XJ Portfolio running on lorry fuel. I know, Jag Diesel is just wrong!

  10. #10
    Junior Member sclayman's Avatar
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    Actually I took the car to the dealer again today, as I had a follow-up appointment to the sunroof fix. Last time they fitted the sunroof kit, this time I understand they will do some adjustments to stop air coming in at the back of the sunroof when travelling at high speeds.
    They will also look at the In Control Apps not working reliably and the iPhone disconnecting from the car after 2 or 3 minutes. More software issues - ha ha!

    I told them about that fuel tank sensor event, and they said they will look.
    2016 X351 XJ 3.0D

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