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IS250 0.23A parasitic drain through MPX-B fuse

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Having been like this since I brought the car back in 2017. Didnt realise that untill currently Battery flatten and changed.

I change the Battery in 2018 with the Bosch S4, which is an decent one. It was flatten a few month ago (April 2020) due to not driving for 2 weeks during the first lockdown. Found a parasitic drain at around 0.15A but i couldnt locate the drains.

In Oct 2020, the Battery is flatten again and I decide to change a new one.

Beside the drain, I also measure the capacity of the 2 year old Bosh S4, which can only hold 20Ah now (marked 70Ah). It indicates that during the 2 year, the Battery has been draining so much from time to time. (Pb Battery will lose capacity very quickly if it always be used > 50% of its capacity)

After that I start to investigate again for the parasitic drain. The first thought was my insurance black box, I found it and unplugged it.


Drains from MPX-B:

Then I measure the parasity current. It is 0.23A, whith most of them throught MPX-B fuse in the engine bay.

Beside the current, I also measure and record the voltage changes in 24 hour, which change from 12.45 to 12.3V. All voltage measuremnet were taken after the car was sit for a day, and door lock for 3 min, so it is pretty accurate.

0.15V change means around 10% Battery capacity which is 7Ah. 0.23 x 24 = 5.52Ah. So I can prove that the 0.23A is continually draining by something when I (the key) was not around.

But the MPX-B fuse leads to a massive problem, it provide the power to many ECUs, which is so difficult to locate.

I assume one of the sensor is preventing one of the ECU to go to sleep so to cause the 0.23A drain.

Lucky, my friend has drop me the repair manual (DVD) for the car. Here are some screenshots from it.  But still checking every ECU is an nightmare to me becasue I living in a flat and cannot bring my PC to the car.

Last night i notice my glove box's ligth wont turn off when I close it. But it dose turn off when I stop the car. Is there a sensor to detect the whether the glove box is closed? The light is LED so if there isnt a sensor, I am ok with it.

The previous owner has change most of the lights to LED including the trunk's light, door lights, and the rear dome light. Not sure they can cause the issue becasue none of them light up when they shouldnt. 

Do you guys have any experience fining the MPX-B related parasitic draining?





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2 hours ago, Aircheese said:

All voltage measuremnet were taken after the car was sit for a day, and door lock for 3 min, so it is pretty accurate.

Not accurate enough I'm afraid.

You need to open all doors so that you have access to anywhere you need but you have to trick the car into thinking that they are closed and locked so that no internal lights come on etc., but the alarm goes into 'armed' mode.

After that, you need to leave the car alone and do nothing whatsoever to it for about an hour, so that all systems that can go to sleep do so and only then will you get a true reading of the quiescent current draw for the alarm, radio presets etc., etc.

Also, when looking for the fault don't take out any fuses because this (or replacing them) could wake up other systems and again you'll have false readings.

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