[MrSweet1991]

Hi All,

With the weather getting much colder I've noticed slower cranks but more importantly my battery is around 11.8v so a module probably isn't going to sleep properly (I have brand new alternator and battery already) so I was wondering how to do a check as mine doesn't have an IBS which I could have just used ISTA to put the car to sleep and check which module is drawing power. Do I just disconnect the negative battery and place my multimeter to positive battery terminal and chassis ground after putting the car to sleep with ISTA+ and any ideas what the correct draw should be when the car is fully asleep? I intend to pull fuses until it drops to the correct reading and then go from there

[Andystobbs]

I'd start with the TCM.
Has your new battery been registered to the car?

You need to flick the doors and boot catch if you intend to work inside the car with it locked and asleep.

You connect your multimeter inline, so one probe on the battery post (either one) and the other one on the lug that you just took off the battery. Could easily be in the order of 5-10A at first but should drop to less than 50mA once its all asleep.

[gIzzE]

I wrote this for the Range Rover forum, but same applies, obviously if you have INPA etc. you can force the car to sleep, hope it helps a bit...




To test for parasitic drain you need to put a multimeter into amp mode and put it in parallel with the cable, positive or negative, but I always use negative, only because if you do accidentally touch the chassis or something it doesn't matter, far safer. 

The multimeter needs the positive set to the amp socket as seen below..... 








Then set it to 10a, it may be 5a or 20a, but set to the highest first and then move down to more sensitive readings if you get nothing, so 20 first, then 200, then 2000 etc. but 99% of time on these 20a or whatever will be fine.

I open all the doors and bonnet, then push the catches shut so the car thinks they are closed, then put something heavy on the bonnet catch.

You can test before the car goes to sleep, just before sleeping it is usually reading 6amps or so, but you can still pull fuses and note any big drops. But you really want to wait till it sleeps.

Mine goes from 6 amps to around 1 something and then after 23 minutes drops to 0.02amps.

So be patient and wait 25mins before panicking. 





To test the alternator for parasitic drain, they fail a lot on TDV8s.
Undo the big red cable that runs to the charge point on the bulkhead, then place the multimeter cables between the cable you have removed and the point it was attached to.

This should read 0amps. 


If it doesn't your alternator is faulty and causing drain.




To test the rest of the car undo the negative terminal, battery or bulkhead is fine, and put the the multimeter between them.

Let the car go to sleep and see what your drain is. I would say anything above 0.25 is too high and needs sorting. 


If it is higher than simply go through the fuses pulling each one out and seeing how much the amps drop, for me it was the bluetooth and TMC unit that was causing issues.

The bluetooth I knew was dead, but being left in caused drain, the TMC unit I can't see why that was causing it, but pulled it anyway.

Down from 0.9-1.1 amps to 0.02-0.04amps when asleep. 


Battery has gone from causing issues after a couple of days to he point where it can be left for a month or more with no problem.

[MrSweet1991]

Originally Posted by gIzzE

I wrote this for the Range Rover forum, but same applies, obviously if you have INPA etc. you can force the car to sleep, hope it helps a bit...

To test the rest of the car undo the negative terminal, battery or bulkhead is fine, and put the the multimeter between them.

Let the car go to sleep and see what your drain is. I would say anything above 0.25 is too high and needs sorting. 


If it is higher than simply go through the fuses pulling each one out and seeing how much the amps drop, for me it was the bluetooth and TMC unit that was causing issues.

The bluetooth I knew was dead, but being left in caused drain, the TMC unit I can't see why that was causing it, but pulled it anyway.

Down from 0.9-1.1 amps to 0.02-0.04amps when asleep. 


Battery has gone from causing issues after a couple of days to he point where it can be left for a month or more with no problem.

Great write up, so you remove the negative terminal from the battery and connect the positive and negative multimeter probes to the negative post on the battery to negative power lead?

Mine drops quite a but by the morning but not enough to prevent the car starting, even on freezing cold mornings so I've been a bit lazy with it haha.

[gIzzE]

Originally Posted by MrSweet1991

Great write up, so you remove the negative terminal from the battery and connect the positive and negative multimeter probes to the negative post on the battery to negative power lead?

Yeah. Basically you are putting the multimeter inline with the battery terminal.
DO NOT START THE CAR!

You then want to let/make the car sleep.

See what amps it is drawing.

Then pull the fuses one at a time and see which ones lower the drain/amps.

This will allow you to track down what it is that is causing your drain.



You will need to close the latches in the door, boot etc. so it thinks they are closed, and put something on the switch for the bonnet too so it thinks that is closed as well.

Make sure all lights are off as well, including interior ones, they should turn off anyway, if not you need to think why not?