Disconnecting the battery on a P38

I have seen nightmare stories of things that have happened to P38's that have had their batteries go flat. There are stories of alarm problems and all sorts of other "quirks" resulting from doing this.

I need to remove the ECU on my late '99 DSE, and to do that (sensibly), the battery should probably be disconnected first.

Am I likely to have loads of problems when I reconnect the battery or is it all a load of old wives tales and I will have nothing to worry about ?

From my experience i left my 02 4.6 with the battery disconnected for a week whilst i changed the engine. before i disconnected i made sure the LED had gone out on the sat nav drive and then disconnected. on reconnection the car started first turn of the key all i needed to do was reset windows/sunroof. But i was nervous that i would have trouble with alarms/locks.

Which ECU do you need to remove??

Problems arise when the battery has gone flat ovr a period of time rather than just disconnecting it, so, remove negative first and then positive and you should be fine.

-Wills

The Becm really needs the battery disconnecting,but all the rest are fine just with the key out as long as you are careful - saves reseting all the windows,radio etc.

wills said:

Which ECU do you need to remove??

Problems arise when the battery has gone flat ovr a period of time rather than just disconnecting it, so, remove negative first and then positive and you should be fine.

-Wills

Click to expand...

I need to remove the Bosch Motronic box so I can chip it. Is it OK to "hot-swap" that one ?

The Motronic is fine just with key off,where is the chip coming from ?

eightinavee said:

The Motronic is fine just with key off,where is the chip coming from ?

Click to expand...

It's made by a company called DAP which I believe is dutch ?

Supposed to give 165hp so we'll see......

On the plus side, it looks like it's blown into an off-the-shelf cmos prom (27c256 I think) which opens up a lot of possibilities

I have suffered two flat batteries over recent months, the first was a dead battery and the second time it was drained by some earth fault. On each occasion, there were numerous alarms raised and recorded but no actual problems.

Dave