LexBrett2

Hey All,
I have a curious problem that I wondered if anyone else had experienced. I'm testing for parasitic draw with my multimeter, but after allowing time for the car to sleep the multimeter "wakes up" the car and I cannot do the test.

Specifically, I disconnect the negative battery terminal, connect red end of meter to cable and black to top of battery, and am looking for a milliamp draw of greater than 50 to confirm parasitic drain is killing my battery.The digital multimeter has a battery in it, and as soon as I make the connection the care wakes up! My only thought is to use an analog multimeter?

Has anyone had this experience or can share suggestions? THANK YOU very much in advance and have a great day!
-Lex

mbmg

I bought a AC/DC Current Mini Clamp tester that uses inductance to measure amp draw. It does so passively so it won't cause the car to wake up. Mine cost about $50.

LexBrett2

So it sounds like you had the same problem? And your mini clamp tested avoided haing car wake up? Aside from some measurement error, anything wrong with using analog meter? Have already bought 4 multimeter, and want to avoid another lol

mbmg

Yes, my mini clamp tester avoided the car waking up. I only show about 3-10 mA draw and it isn't constant (it's like it is "pinging" sensors). Most of the time it reads zero mA draw. I think you should be fine using an analog meter if the amp rating is large enough. I kept my mini clamp tester in the 2 amp range for resolution but if you have a large amperage draw you would want a tester to be able to handle that amperage or it will blow it's fuse if it has one or damage the tester.

rbm

The meter you are using may be overloading the circuit because of its burden voltage. If this is the cause and since you want to measure such small current draws, you should get something like a uCurrent GOLD Multimeter Adapter. It isolates the load presented by the meter. Or you could try and find another better quality meter with a lower burden voltage spec.

scotterikson

The meter completes the circuit, which wakes up the car. Just leave it connected and monitor for a few minutes. There will be a couple drops in the draw as the car "powers down"

LexBrett2

Hey All, Thanks so much for chiming in on my parasitic draw issue. I feel like analog is the way to go. Once I establish a baseline draw, I will pull fuses and look for a drop. Since my car dies in about 12 hours, I expect to find a fairly large draw and a noticeable drop when and if find the circuit in question. Below is the link to my multimeter; the setting seems really straightforward for what I need to do.

bbirdwell

Follow the link to my post describing how differing amounts of current drain indicate the failure mode per WIS. The links are to posts 5 and 7 in the thread.

https://mbworld.org/forums/e-class-w...ml#post7759367

and

https://mbworld.org/forums/e-class-w...ml#post7759633

ot1

...

LexBrett2

well I am going to just use my analog meter this weekend. Less precise, but easier to interpret the dials and will not wake up the car.

LexBrett2

Hey Buddy. I noticed in one of the threads that you referenced that 40 milliamps was the amount of draw that one should expect when car is asleep. I'm getting a 50 milliamp draw, which is a bit high, but should not completely kill my battery in 12 hours. Do you agree??

scotterikson

I'd argue that you want to wake up the car with the meter, how else are you going to find a problem with how it goes to sleep?

bbirdwell

50 mA could be within the margin of measurement error and is not enough to drain a good battery overnight.

LexBrett2

Right on. Thanks for the response. Have a great weekend.

LexBrett2

So I am looking for the parasitic draw when the car is completely asleep. For example, your radio stores codes and the ecu keeps track of the clock time; there is energy being sucked out of the battery even though nothing is visibly on.

The procedure that I have seen on dozens of threads and videos:

• disconnect negative terminal
• connect red side of multimeter to chassis cable and black to terminal
• wait to go to sleep
• look closely at milliamp draw.

This mimics the battery draw when car is not running and nothing is "turned on".

If the car were not asleep then we would not be measuring parasitic draw, e.g., if the interior lights are on if door is open.

DarthBudice

What vehicle chassis is this? A W211 (your profile says a W203 and a CLS)?
If it's your W203, unplug the harness for your power seat modules and see what happens.

bernard farquar

I did the same thing, but the sensomatic brake pump cycled on and blew out my meter.

ot1

That's why its better to get a clamp style amp meter.

007_e350

I had front SAM faulty causing 1 amp of draw every 15 mins ..there is a recall on it .. but I ended up losing the car due to to this

taylor210

Where can we find more info about that recall? I also have a power draw from driver seat module.

thank you!