Testing for slow battery drain W211

[Austy]

Hi Guys. I think I have a slow drain, battery would be flat if left for even just 1-2 days which imo shouldn't be normal regardless of the amount of electrical systems in the car (Alternator and battery are fine).

I tried to test for a drain with a multimeter (set at 10A DC) and pulling fuses 1 at a time. I obviously needed the boot lid and driver door open so I manually closed the boot and door locks, and clamped the interior light button on the drivers door pillar. Locked the car and left to rest for an hour.

When I came back to the car to perform the test I removed the negative cable from the battery and connected the multimeter in series. This caused the indicators to flash which obviously caused flux to the readings rendering test useless. I didn't see the indicators at first but I could hear the fast click from the dash, they were flashing fast as if the alarm was activated (alarm was prev disconnected as it causing a key fob locking issue)

Have I missed a trick somewhere? Is there something else I should/shouldn't be doing? Any advice appreciated.

 

[Westheath]

Test both batteries
Remove them from the vehicle,
put on charge over night and then have them checked.

 

[Austy]

Test both batteries
Remove them from the vehicle,
put on charge over night and then have them checked.

Thanks Westheath, have done and they're fine. Was wondering more along the lines of the process I followed for testing the amperage, and the flashing indicators - should I have the deactivated the motion sensor at the interior mirror?

 

[LostKiwi]

Yes you need to deactivate all sensors for the alarm to prevent it triggering. You also need a DC clamp meter to measure current as the moment you disconnect/reconnect anything you invalidate the test as CanBus wakes up.

 

[M80]

Would the control units still go to sleep with the bonnet up?

I can see the clamp being useful, then by pulling individual fuses if the current is higher than should be, but at low currents I've not found DC clamps to be accurate. Then they tend to read differently if reverse clamped.

 

[Austy]

Yes you need to deactivate all sensors for the alarm to prevent it triggering. You also need a DC clamp meter to measure current as the moment you disconnect/reconnect anything you invalidate the test as CanBus wakes up.

Thanks LK. I don't have a clamp meter at the minute. If I disconnected the battery and left it disconnected for a period would the CanBus go back to sleep?

 

[Austy]

Would the control units still go to sleep with the bonnet up?

I can see the clamp being useful, then by pulling individual fuses if the current is higher than should be, but at low currents I've not found DC clamps to be accurate. Then they tend to read differently if reverse clamped.

Thanks M80. I didn't have the bonnet open, I was going to try boot and drivers side fuse boxes first as I've a sneaking suspicion it's Comand related.

 

[LostKiwi]

If you suspect Comand just pull the fuses for it and see if the problem goes away.

 

[Oldspanners]

Thanks M80. I didn't have the bonnet open, I was going to try boot and drivers side fuse boxes first as I've a sneaking suspicion it's Comand related.

Have a look at this video very comprehensive explanation with very helpful charts on voltage drops across a fuse.

 

[M80]

Have a look at this video very comprehensive explanation with very helpful charts on voltage drops across a fuse.

If you see a voltage drop across a fuse there is an issue with one of the connections to the fuse, or it's blown and you're measuring a volt drop through the meter.
Any conductor of such a short length shouldn't show any resistance we can measure, or it would get warm (at least, - depending on the resisitance and the curent it is passing).
I didn't see all 10 minutes but wouldn't trust that tutorial to help here.

What is needed to measure is the current passing through a fuse, for that withdraw the fuse and bridge the contacts with the meter set at highest current setting, and drop down the range for more accurate measurement.
With access to the wiring a clamp might well do ok, but stray fields and 'my' experience of innacurate DC clamping might skew the result.

I was assuming here that the battery was under the bonnet, so concerned that the car wouldn't go to sleep. The video suggestion of 'cheating' the locks should be a good 'frig' though.

Some time ago I adapted a blown fuse that I could connect my meter to, so just moving the fuse around to see the current in that circuit.

 

[Oldspanners]

If you see a voltage drop across a fuse there is an issue with one of the connections to the fuse, or it's blown and you're measuring a volt drop through the meter.
Any conductor of such a short length shouldn't show any resistance we can measure, or it would get warm (at least, - depending on the resisitance and the curent it is passing).
I didn't see all 10 minutes but wouldn't trust that tutorial to help here.

What is needed to measure is the current passing through a fuse, for that withdraw the fuse and bridge the contacts with the meter set at highest current setting, and drop down the range for more accurate measurement.
With access to the wiring a clamp might well do ok, but stray fields and 'my' experience of innacurate DC clamping might skew the result.

I was assuming here that the battery was under the bonnet, so concerned that the car wouldn't go to sleep. The video suggestion of 'cheating' the locks should be a good 'frig' though.

Some time ago I adapted a blown fuse that I could connect my meter to, so just moving the fuse around to see the current in that circuit.

You need to watch the whole video.
Measuring the voltage drop in mV across the fuse which has resistance as the weak link in the circuit and using the chart to calculate the current draw.
Taking a fuse out to measure the current directly will lead to "waking up" some components elsewhere and ruin any further investigation.
It's up to you the information is all there.

 

[Austy]

If you suspect Comand just pull the fuses for it and see if the problem goes away.

I do pull the 5amp Comand and 7.5amp CD Changer fuse overnight, but not sure if it makes any diff because I'm driving the car everyday at the minute (varying distances too so can't really log the voltage each morning as previous day it might not have went too far, other days I'd be doing 100s of miles). Just want to try and get to the bottom of the problem before the next time I have to leave it sitting up for a few days

Should I disconnect the battery before I leave the car to go to sleep?

 

[Milu]

I've used the mV test as above rather than the amp test because as noted when you connect a meter in series it wakes up the car and you have to wait again.
The mV method with the relevant chart is easy and useful

 

[M80]

I take it back,
I didn't see how we could test for a volt drop across what should be a dead short, but it works.

Using my regulated supply a passed a current to a 12v 20w lamp and measured across a 5 amp fuse, my reading were higher than the chart but close enough to be of value,
reducing the current in the cct reduced the volt drop.

Old dog, new trick, still surprised.

 

[LostKiwi]

I take it back,
I didn't see how we could test for a volt drop across what should be a dead short, but it works.

Using my regulated supply a passed a current to a 12v 20w lamp and measured across a 5 amp fuse, my reading were higher than the chart but close enough to be of value,
reducing the current in the cct reduced the volt drop.

Old dog, new trick, still surprised.

It works because a fuse has a very small resistance, slightly higher than a simple piece of wire. It's the voltage drop across the resistance we measure.

 

[Steve@Avantgarde]

Being a 211 I would start by disconnecting the phone control module. Usually the source of all drains on 211's.

I would buy a cheap amp clamp meter, a great way of measuring used amperage.

 

[M80]

Just be sure it's a DC clamp, most are AC only.

NKTECH Digital Clamp Meter Auto Range Voltmeter Amperemeter Ohm Test Multimeter | eBay

 

[Austy]

Being a 211 I would start by disconnecting the phone control module. Usually the source of all drains on 211's.

I would buy a cheap amp clamp meter, a great way of measuring used amperage.

Thanks for the advice. I will def look into this, it isn't used so I won't miss it. It's the old Nokia system and the car came with a Parrot fitted. Gonna look for some info on the site for how to go about this.

 

[Austy]

Brief update on how I've got on so far. Finally got a look at the car last weekend to check for the source of the battery drain. I Used the fuse method as post above (thanks OldSpanners!) and it worked a treat.

Fully charged the battery and put it back into the car. Opened the drivers door, bonnet and boot lid. closed all the related locks and deactivated the interior motion sensor. Locked the car and left to rest.

Started off checking the fuses in the drivers side. I knew the Comand unit was offline as it occasionally does (shows the Star badge if u press the power on button). It has been doing this intermittantly since i bought the car last March. This is why I suspected it may be related to battery drain. I feared it was drawing power whilst showing no signs of life, also whilst driving and switched off it would make a noise every few minutes similar to that of a cd player trying to read a disc.

None of the fuses in this box showed any usage except the 5amp Comand fuse. I could hear the disc noise as noted above. Checked under the bonnet and all fuses fine. Finally went to the boot where I immediately heard the sat nav in operation. Obvious red flag. Tested the fuse whilst still in operation and of course it was drawing power. Sat nav then powered off. I had my fone handy so i decided to start a timer in case this wasn't a one off. It started up again. Measured it a few times and approx. it was taking a 2m10s break then running for 1m30s. Whilst it was powered down there was no draw through the nav fuse in boot.

Tested the Comand fuse as I suspected I had just got lucky the first time I checked it. I was right. Whilst the sat nav was powered down the Comand fuse wasn't showing any power usage and couldn't hear the disc noise.

When I did the mv to ma conversion shown in the vid the two items combined were drawing approx 1.5amps and the draw is for approx 10 hours per day (nav power on and off timings extrapolated) so would you agree this is sufficient to cause a 019 battery drain over 1-3 days?

I was running out of time so I pulled out both the nav fuse in the boot and the comand fuse at drivers side and the battery voltage has remained very high all week.

I know very little about this kind of thing so apologies for any silly questions. I was wondering which unit is causing the other to come to life - 1. is the Comand unit sending a signal to the nav to cause the power ups? or is it the other way around? maybe the source comes from somewhere else e.g. AGW?

Is my cheapest fix to fit a fibre optic loop to the nav and pull the power source out? If it gets the radio to work reliably I'd be happy enough, it's a 15yo car in fairness although it's in very good nick otherwise with just 80k.

All advice appreciated and thanks in advance!

 

[LostKiwi]

would you agree this is sufficient to cause a 019 battery drain over 1-3 days?

Yes over three days.