Discuss E39 530i touring - Nav fuse stray voltage on earth side - battery drain in the Auto Electrician Forum area at ElectriciansForums.net

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I have recently traced what I think is probably causing my battery drain to fuse 56 in the boot of my touring which is one of the navigation fuses. I thought could just pull the fuse to stop the drain as I never use the sat nav anyway but its had some other consequences.

When I pull the fuse the instrument cluster doesn't show the blinking green lights when i use the indicators, or the blue light when I flash high beam. These lights are still working on the outside of the car, i've just got no indication that they're working from inside the car. Also my reversing lights do not work. These problems all go away once the fuse is plugged back in. I wouldn't have thought that fuse would affect the lights. Those systems are all on the I-bus but can't see how that shoud happen.

I thought I would check the fuse terminals and for fuse 56 I get 13V the live side and 0.5V on the other side. All the other fuses I tried have 13V and 0V. Could this 0.5V be the cause of all the problems and if so how do I go about resolving it.
Nothing related to any of this showing on fault codes.
Any advice much appreciated.
 
Hi,are your fuse voltages measured at the top of an inserted fuse,or,from the fuse board receptacles?

I would look for a drain using current,not voltage measuring equipment.
 
I used the multimeter inline on current to determine that there is in fact a drain. The car is drainwg 70-90 mA after it goes to sleep and it should be no more than 40. Ive got a suspicion the Sat Nav is waking up every now and then which is why I took the fuse out and then I decided to check the voltage there and that's when I found voltage on the consumer side of the fuse terminal. Thats with the fuse removed.

I've already tried waiting for the car to go to sleep and removing fuses one by one to see what the current draw does but this does not has not yielded much.
I'm going to unplug each pieve of equipment fed by that fuse next and see what happens.
 
even 100mA on a 60Ah battery would take 3 weeks to totally drain the battery.
 
I thought I would check the fuse terminals and for fuse 56 I get 13V the live side and 0.5V on the other side. All the other fuses I tried have 13V and 0V. Could this 0.5V be the cause of all the problems.
Your 0.5V does not prove a fault with no fuse present.
a) It could be leaking from another powered circuit ..BUT..
b) It is more likely to indicate delicate electronics are present.
c) These electronics have reverse polarity protection
(wastes 0.4 V to a high impedance )
d) Some electronics have Capacitors that retain a little power.
-----
40mA is not much ! (unless it worstens )
 
SUCCESS!
So I've just unplugged the SatNav unit and the voltage on the consumer terminal on fuse 56 went from 0.5V to 0.08V. I've just left the multimeter connected to the battery and waited for the car to go to sleep and after 16 minutes its drawing between 30-40mA which is bang on spec.
 
You have to remember that there are components that require a stand by voltage , like the permanent radio memory supply, and the alarm system, there are more depending on the sophistication of the accessories.
Have you had the alternator output checked and the tension on the drive belt?
Have you had the battery checked at a facility with accurate and dedicated equipment?

Sorry I was typing as you posted. But as @telectrix , that draw would not discharge your battery in a short period of time.
 
Last edited:
Hi,
I have not had the battery tested, but it has now been flattened a few times because of the draw, it was a year old and 100Ah. I put a new one in it yesterday, eaxacly the same as the old one, so I can rule it out as an issue. Voltage goes up quite high when the engine is running so it is definitely charging.
I'm convinced I have found the piece of kit causing the problem, although I dont actually know whats wrong with it. Presumably it could be a wiring porblem as well rather than the equipment itself.

That draw was OK for about a year (when I put the last battery in) and obviusly killed it over that time period as I only drove the car every two weeks. But when it did get driven it was two long journeys of 70 miles each over the course of the day, so it was getting charged properly each time.

I suppose I should try another Nav unit in there and if the problem remains its in the wiring, and if the problem goes, it was a problem with the original unit.

Just been out and tested a few things with the multimeter and some strange things going on.

Brand new battery car off: 18.7 V
New battery engine on tickover: 20.7 V
1500 rpm: 21.9 V
2200 rpm: 22.1 V
3000rpm: 22.3 V

So I think voltage regulator is broken, But

Old 'flat' battery: 18.8 V
So is the multimeter knackered??
 
something is knackered. even with engine running @ 200 rpm, voltage shoud not be above 14.2V, give ir thake 1/4 of a volt.
 
Probably your multimeter, an ECU should shut down above 18 volts to protect itself.
The ECU has upper and lower operating voltage limits.
 
Hi,
I have not had the battery tested, but it has now been flattened a few times because of the draw, it was a year old and 100Ah. I put a new one in it yesterday, eaxacly the same as the old one, so I can rule it out as an issue. Voltage goes up quite high when the engine is running so it is definitely charging.
I'm convinced I have found the piece of kit causing the problem, although I dont actually know whats wrong with it. Presumably it could be a wiring porblem as well rather than the equipment itself.

That draw was OK for about a year (when I put the last battery in) and obviusly killed it over that time period as I only drove the car every two weeks. But when it did get driven it was two long journeys of 70 miles each over the course of the day, so it was getting charged properly each time.

I suppose I should try another Nav unit in there and if the problem remains its in the wiring, and if the problem goes, it was a problem with the original unit.

Just been out and tested a few things with the multimeter and some strange things going on.

Brand new battery car off: 18.7 V
New battery engine on tickover: 20.7 V
1500 rpm: 21.9 V
2200 rpm: 22.1 V
3000rpm: 22.3 V

So I think voltage regulator is broken, But

Old 'flat' battery: 18.8 V
So is the multimeter knackered??

The easiest way to prove your multimeter is reading correctly is to try another one. Don't run your car until you know that the charge voltage is correct as you will likely damage things.
 
Brand new battery car off: 18.7 V
New battery engine on tickover: 20.7 V
Been there with a DMM reading too high.
If you can find.
A few 1 inch fresh lithium cells 3-3.2 Volts each .
a fresh 9V battery never much more than 9.6 - 10V NEW
.or an old USB cable((plug into Charger (red/black)) ..4.8-5.3V
...
Side light bulbs will all probably look all silvered (black on glass)
if have really over volted things.
 

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