2001 S-Type 4.0 - Finding Parasitic Battery Drain

I went through a few new 49C batteries that went dead after just a few weeks and thought they had to be faulty. Then I was told that I must have a parasitic battery drain somewhere in the electrical system. I got a battery charger/maintainer which now keeps me consistently on the road, but it’s time to try and figure out what and where the battery power is going. I don’t even know where to start, so I’m reaching out to the forum. Any thoughts? Also, after the car sat for a few weeks after the first severely dead battery replacement, the built-in phone quit responding. That’s probably another forum topic, but thought I’d mention it. Thanks for any help.

Welcome to the forum Steve.

First thing you are going to need is a digital multi meter.
Disconnect the negative battery lead and connect the DMM leads to the battery and negative leads with the DMM set to milli amps.
You will need to leave access to the fuse boxes open which may require doors, bonnet and boot to be open.
After a period of time the computers will go to sleep and you will observe a drain on the battery.
You now need to start pulling fuses until you find the circuit that shows a drop on the draw on the battery. You are looking for a total drain in the region of 30milli amps from memory.
Once you have identified the circuit thats causing the problem report back and we might be able to nut out what’s happening.

Thanks very much for your quick reply, Robin. Will an analog multimeter work, or should I go ahead and buy a digital one before starting in on this project? Also, are there more fuse boxes besides the one under the hood on the passenger side? Thanks again.

Hi Steve, not sure on the S regarding the fuse boxes but on my X308 there are fuse boxes for Africa, one each side in the rear foot wells 2 in the engine bay and another in the boot.
I don’t think you will get the resolution with a analog MM but you could try it.

It takes 40+ minutes for the X200 to ‘power-down’ to a nominal 30ma. (go to sleep)
This length of time made it very difficult to find power drains on these cars when I worked at the dealer.

The initial power draw at shutdown is somewhere in the 4 to 5 amp range and the draw drops incrementally over the 40+ minute ‘power-down’.

The X200 is susceptible to water collecting in the boot and damaging modules so be sure to check.

Some people have reported faulty ignition switches causing a drain.

The SCP network might have a problem with a module?

I see more diagnosis in your future.

Ouch thats a hell of a time frame :slightly_frowning_face:

I also measured around 30mA on my 2000 4.0l but to make the final ‘fully asleep’ quiescent current measurement, I found the car needed to be locked (which sets the alarm) and you have to leave the meter outside the boot to make the measurements. You can’t have it inside because as soon as you open the boot lid the modules start to wake up.

Incidentally, in theory, a 90AH battery should be able to supply 30mA for about 3000 hours. However, you have to de-rate this by quite a bit to get to a period of time that you can leave the car and it will still start.

Four or five weeks is probably the practical limit.

You can trigger the boot closed situation by flipping the catch with a screwdriver. You could possible do the same with the doors so that the car thinks its closed up and will lock? I know the boot works as I have done that when I had the battery on charge with the electric cord going into the boot and not allowing the lid to close.

TheX200 (2000-2002) has a BUTTON that needs to be depressed to signal BOOT CLOSED so I used to use a plastic windscreen tapered end stick routed through the sealing rubber to keep the button in the OFF position.

This allows the boot lid to remain open while all the testing is being done.