Window modules have very short memory

[Simpo Two]

2007 DB9. Over the last month or two, the 'auto-drop' function of one of my windows has stopped working. Sometimes it's the passenger door, sometimes the driver's door. Each time I pull the fuse, put it back, and it works again. But then a week or maybe less later, the function stops again. At first I thought it had happened because I opened and closed the door quickly after driving off and that had confused it. But it's still doing it, and maybe a coincidence but it seems worse when the car's been parked in the sun.

I'm getting rather tired of grovelling in the passenger footwell; is there a fix please? The modules are working, but just keep forgetting.

[Simpo Two]

Hmm... perhaps...

What we need is a diode or some sort of gadget in the line to stop the voltage dropping on start-up. Seeing as you're my electronics guru, can you make me one?

[Simpo Two]

ctdctd said:

I can - it will be £500 delivered, easy self install. Payment in advance, no refunds.
Gizmo box will be exactly the same size, fit in exactly the same space and use exactly the same connections as your existing old battery.
In fact, the only difference you might notice is that it will be new!

For £500 you can supply and fit it and buy me a steak supper and some cases of fine wine!

Is a battery swap something that Halfords can handle? I know they have a special battery fitting area, but settings like misfire corrections and probably other things will be lost - or do they keep a 12V feed somehow?

Resetting misfire corrections is highly hazardous because the roads are so busy.

[Simpo Two]

Has anyone used Halfords for a battery swap, and if so did everything work as afterwards?

[Simpo Two]

paulrog1 said:

You can replace the battery, very easy to do, just need to carry out the relearn of windows and seats, take the car out first thing on Sunday morning into the countryside and find a long straight road.

The only road round you could do that on round here on is the A12, and last time I got rather tired of being hooted at by irate motorists as I was trundling along at 21mph... bloody dangerous. It takes a stupendous amount of distance and time to coast from 70mph. Three times.

https://aston1936.com/2016/03/18/relearning-the-mi...

What other car requires that sort of nonsense after a simple battery change?

Would I be right in thinking that most people don't bother with it (or more likely don't know about it), carry on regardless and everything works fine?

[Simpo Two]

Interesting, thanks. So it's not that misfire corrections are lost, but that the misfire monitor is deactivated?

Misfires don't seem to trigger any warnings or leave codes, that's why people can worry so much about them.

paulrog1 said:

I think what happens at service in a dealer garage or an inde with AMDS is the misfire monitor settings are transferred to AMDS if the battery needs disconnecting and uploaded back into the car afterwards.

That suggests that something IS lost...



I can physically replace the battery, but it would be my luck if it didn't start afterwards for some reason!

[Simpo Two]

paulrog1 said:

It's both - the misfire info is lost and the system is deactivated.

And yet the engine will not run any differently and ignition timing and fueling trims will work the same...

The only way to reconcile both facts is to conclude that data is lost but it's irrelevant...!

[Simpo Two]

I see - so the idea that it applies 'corrections' is wrong. That must be it.

Thanks for your patience!

So in conclusion, if the battery is changed and I don't do the rundowns, the only difference is that the car won't tell me if there's a serious misfire, is that right? They can of course be read using live data on AMDS or suitably equipped Foxwell.

[Simpo Two]

paulrog1 said:

The AMDS or Foxwell cannot see the misfire monitor

No, but misfires can be seen live, my local garage did it with a Foxwell.

Unless the car needs some other work done I'll let Halfords do the change. £135.99 would be the second-lowest bill I've had for the car, and that includes the mobile fitting service (saving a gallon of petrol!) And if something goes wrong they get to sort it out, not me.

Thanks for explaining the position which enables me to make an informed decision