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.

[ctdctd]

I know nothing of these DB9's of which you speak, but I'd put 50p on it being the battery on its way out.
When you start it, the voltage drops enough for the modules to get confused.

[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?

[steveatesh]

ctdctd said:

I know nothing of these DB9's of which you speak, but I'd put 50p on it being the battery on its way out.
When you start it, the voltage drops enough for the modules to get confused.

This.
It happens on my Vantage and the battery on that is on the way out. Sadly the car isn’t get used much now at all (even the MOT and Service guys comment), and the battery suffers accordingly.

[-jester-]

As others have mentioned, an old battery can cause problems with the window modules but they are also prone to failing on older Gaydon models (both DB9 & Vantage) if pulling the fuse and resetting the module doesn't seem to work or if the issues persistently reoccur you may need to replace your window modules.
In 2009 Aston updated the window modules which are supposedly better.

Here's Mike from Bamford Rose to explain it better...

[ctdctd]

Simpo Two said:

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?

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!

[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?

[paulrog1]

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.

Regarding the window modules, the early cars did have problems, both with the window modules and central locking issues, sadly the only way of a repair is to get them replaced.

Edited by paulrog1 on Tuesday 2nd July 15:43

[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?

[paulrog1]

Simpo Two said:

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?

You are right, it is complete nonsense, I don't know any other cars that need to do this, I read somewhere when Ford developed this V12 they were (at the time) at there limits with the engine control system, who knows. Plus I think owners don't bother either, remember it is a misfire monitor, the engine will not run any differently, ignition timing and fueling trims will work the same, the only difference is when the misfire monitor is active and if a really serious misfire is going on the engine management system will know about it and (I think) put the car into limp mode and give you an emissions warning.

The engine management system after a battery disconnection forgets the short and long fuel trims, once you give the car an initial drive around normally the fuelling trims will be set, although they do change depending on the engine revs and the vacuum inside the inlet manifolds, the lambda sensors in the exhaust manifolds tell the engine management system how well the combustion is and the fuel injectors adjust the fueling to suit as the engine will always want to get as close to Lambda 1 as possible.

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.

Edited by paulrog1 on Tuesday 2nd July 16:44

Edited by paulrog1 on Tuesday 2nd July 16:55

[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!

[paulrog1]

Simpo Two said:

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!

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

With these cars the misfire has to be severe for the system to react and an emissions warning is shown

At a garage, the misfire info is downloaded to AMDS, then uploaded back into the car afterwards, so that info is not lost.

[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...!

[paulrog1]

Simpo Two said:

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...!

The misfire monitor is program in the engine management system to alert the driver when a very severe misfire is occurring.
The data is lost when the battery is disconnected and gained when successfully completing the rundown procedure.
The misfire monitor program does not affect how the engine runs.

[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.

[paulrog1]

Simpo Two said:

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.

The car cannot "correct" misfires, the sparkplugs either spark....or they don't. I believe the system works by the ECU monitoring variations in the crankshaft speed through the crankshaft position sensor. The ECU knows that there is supposed to be a power impulse every time a cylinder fires.The only reason there is a misfire monitor is because it's a legal requirement not to exceed emissions requirements, not to protect the engine or cats.

The AMDS or Foxwell cannot see the misfire monitor if the battery has been disconnected and the misfire monitor settings have been lost, the dealer or inde will just take it for a drive for a few minutes down suitable roads, that will successfully enable the misfire monitor program, they'll then come back and connect it to AMDS to see the live misfire data.

Your fine to replace the battery, recalibrate the seats and windows then let us know how it's gone.

Edited by paulrog1 on Tuesday 2nd July 21:20

[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

[paulrog1]

Simpo Two said:

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

Yes, because your misfire monitor on your car is currently enabled.....it will be disabled and settings lost after your battery is disconnected.....you will need to perform a rundown procedure to enable the system, after that your foxwell will give you the misfire rates.

[AMV8Stuart]

I'm sure I've seen people saying that they connect a charger during the battery swap to retain settings/misfire data. Obviously care needs to be taken to ensure the live terminal when removed from the battery is isolated but sounds as though it would work.