Hi everyone,

I've been enjoying the forum as I get to know my 01 XJR.

In reading through the past threads (Dare I say most of the 200 pages) every once in while like last week there is a thread on the hard reset, reboot - whatever we call it. Touching battery cables together.

Now I can understand if there are stored memory items in a register regarding fuel map etc. This is what I want to know:

Other than witchcraft what benefit is FACT regarding this procedure. What does it actually accomplish?

Thanks in advance. This is one area where there seems to be empirical evidence that this is a beneficial solution, yet no agreement here. Can someone please outline the factual benefit?

Thanks

Josh

 

What happens when you restart your pc or unplug power from your modem...yep same thing. It just restores factory defaults in ecus with volatile memory. Its the only thing you can do to do a system restore or restart on a car. Todays cars especially all luxury cars are very adaptive/learning, and sometimes they learn stupid stuff or adpat to mask or adapt to problems like air to fuel paramerters say from a vacuum leak. if you fix the vacuum leak and the long term adaptations have changed, you need to clear them out or youll have a new set of issues without actually having a problem. Its just using learned info and made changes that are no loonger relavant and will cause issue that wont be corrected fast enough to relearn. No voodo

 

Ok,

I can buy that - I guess I would expect an adaptive system to self correct if said issue is resolved? But maybe that is an unreasonable expectation.

Should one embark on the reboot, what will be needed such as security radio codes etc.?

Also, in your opinion is there any value as doing this avery XX,XXX miles as a preventive approach, or is it simply a last resort as part of corrective action?

Thanks for the replies.

 

No only when needed cause there are good things that adaptive strategies do.

 

My 1drivers side window would not lower with the switch. reboot fixed it. That is the ONLY problem I have EVER resolved by a reboot on 3 different x308s.

 

How it's done correctly? touching the negative ground cable to positive? or??

 

This is going to do absolutely nothing. I don't get the fascination with this myth. Disconnecting the battery and grounding the positive terminal does drain all capacitors as well as kill all memory except storage in non-volatile memory...but it does not fix hard faults and will not clear codes. Even clearing fuel trim does nothing as fuel trim is immediately reestablished after restart and warmup. If there was a rich/lean condition, STFT will immediately adapt and LTFT will be adjusted right back where it was.

 

But in some cases a reboot helps getting electrical problems solved.

See this thread for example...
https://www.jaguarforums.com/forum/s...ad.php?t=44277


David

 

Nope - simply not true. Disconnecting the battery and calling it a reboot or hard reset is a misnomer. Electrically, you're doing nothing to reboot anything that hasn't been done already by turning the ignition key to the 0 position. This is much more like a reboot which, when the ignition is returned to the II position all major modules are exercised by a startup diagnostics (providing the system is in P1111, that is). This is the only true reboot and occurs every time the engine is started.

Sometimes through a number of indvertent acts such as physically unplugging, connectors, disconnecting the battery, connecting everything back up again the wrong conclusions are drawn that somehow disconnecting the battery fixed the electrical problem when likely the uplugging/replugging of the connector was the real fix.

One major probably unanticipated disadvantage to disconnecting the battery when fault codes are present is that codes are stored in volatile memory and can get erased especially if the capacitors are drained, (become unreadable with a scan tool), not that the problem is fixed, of course, just that now diagnosis is made much more difficult.

 

Steve:
While I agree with the basic premise of your post, as an academic exercise, I argue with two points. First, while the key-on apparently does a reset, it is not actually exactly the same as a power on sequence in that it does not drop all power to all the circuits, And as those of us who have done electrical design know, things do not always work as designed!
And as to shorting the leads- several of the modules I have had the unfortunate experience to have been inside of have a series diode in the power circuit- no doubt to try and save a cross wired jump or such, so even shorting the wires will not discharge the caps and render a zero state.

 

uhhh, NO, Steve have you had coffee yet this morning???
Fault codes are no longer stored in volatile memory since the advent of OBDII
You cannot erase codes by disconnecting a battery. And if this is such a myth..WHY is it now required diagnostic proceedure recommended by Jaguar technical engineering and a step that must be performed as part of K064 2011 XJ enhancment????
Also if a myth why does it fix issue, because theyre SOFTWARE issues and computer lockups...just like what happens occassionally to what youre typing on. On long term fuel trim it does not immediatly reset, only short term cause short term is instant. Long term is adaptive and learned. You must clear long term fuel trims out after many fuel/air related issues are fixed. Either with a hard reset or SDD/IDS.
Heres another 1 for you Im dealing with. I had an issue with license plate lights going out on a 2010 XKR. Problem was loose pins in the bulb connector. Fixed that and the lights still didnt come on..WHY you ask, cause the rear electronic module sensed the fault and turned the circuit off. Now 2 things, I could do a hard reboot and get them back on until it saw the fault again. But even after the fault was fixed, the module had to be rebooted to go back to factory programmed settings and turn the plate light circuit back on. It wouldnt see the problem as being fixed and start working again it needed a RESTART. Just like when you load new software/updates into your PC.
Heres another issue. Body shops leave batteries unplugged and out of cars for long periods of time. Then when theyre hooked back up the window operation is incorrect, things like drives window wont work. Passenger rear goes down when you press drivers rear etc...then you do hard reset/reboot whatever you want to call it. Then all modules begin to properly function again....ok Im done Im going out to the country and mow and drink a beer CHOW...