2007 clk 220 cdi parasitic load

[Stussy]

Hi everyone

Hope your not too busy...

Was wondering if anyone could offer some advice into a rather nasty battery killing parasitic load my car has unfortunately decided to develop.

Started on Friday evening, went to unlock car after work for commute home and it wouldn’t have it.

Used the emergency key to manually unlock and quickly decided the battery was flat, reading approx 5v! that worried me as the battery is a massive yuasa 95ah agm that’s only 6month old.

I pulled it out of the car and went to my local GSF who quickly decided it was faulty and swapped it under warranty for a new one, then returned to the car popped new one in and fired up no bother!

The next morning (yesterday) off I go to start up car and sure as shit exactly the same thing! Same battery voltage of approx 5v

Now my **** really collapsed, 2 £200 Batteries dead within 24 hours! And I’m pretty sure GSF arnt going to be so understanding this time.

So very reluctantly shelve anything else I had planned that day and set about trying to diagnose the load.

Embarrassingly im a electrician so I have a VERY basic understanding of auto Electrics but by no means am I a auto electrician!

First came basic
“have I left anything on” test....erm no.

Moving on Tested alternator with batt lead off and control plug out, diaode test with multimeter checked out ok between the alt casting and batt terminal, approx 550mv one way only...not that then!

Now came the hard bit, as I had a battery that has a useless voltage I borrowed 2 fully charged from a Friend to hook up one at a time to see if we could do a ammeter test.

Once the car had settled down a bit we measured approx 7a load with the key totally out ignition.

Pulled every fuse/relay I could find at the 3 boards and not one significantly dropped the load (down to under 1a total draw).

Bugger!

Unhooked battery and tested voltage...approx 10v

This thing is pulling some serious current!

Next step was to try and start the car to check with my diagnosis tool for any fault codes, we managed to get it going by using 2 batteries in parallel and also a jump starter thrown in for good measure.

Car fires up and runs fine, diagnostics tool only shows codes I was expecting like low voltage faults etc so all clear just fine.

No lights on dashboard to indicate fault either and alternator voltage approx 14v.

While car is running i make sure everything is switched off, lights heater, radio etc. I have a very basic clk with no bells or whistles so this is easy to confirm.

We then switch car off and unhook the battery, we then connect in series a ancient anologe ammeter from a original mini!

This shows a load of 30a!

WTF is going on!

By this time it’s been all day and now very dark so we leave the battery disconnected and call it.

I have a couple of mates that are mechanics that suggested directly unplugging the glow plug module and checking load then and also the blower motor.

I did notice my blower fan going even when I made sure the HVAC was switched off but I assumed it was a trickle mode a sit wasn’t going perticually fast.

Does anyone on this fine forum of mercedes enthusiasts have any idea or advice to offer before this enthusiast loses his enthusiasm?

Thanks in advance!

 

[Edd1968]

Hi there, crap situation and my sympathys.
I had a similar issue, not with a Merc however, with my Ford. I went through the same tests, it turned out to be the heated windscreen relay stuck on and eating a battery charge in 20 mins!
Not sure if your CLK has a heated screen (didn't think they even offered that as an option on '07) but is something showing as off but is actually still on.
Just a thought.

 

[cheddar]

Almost every time on these generation of engines, a large drain like that is caused by a defective heater booster. It’s mounted above the starter motor, and the reason pulling every fuse still doesn’t stop it, is because it tee’s off the starter motor feed.
Common in the colder seasons, especially after the first cold snap. It only operates from cold start when the temperature is below a certain point, it’s just there to warm the coolant up quicker.
Most people just cut the power to it and unplug the control connector.

 

[Stussy]

Thank you both very much for your suggestions.

Is the heater booster on every one of these engines as standard to help it reach temperature on a cold day or is it a optional extra?

I will definitely have a look for it and see if I can disconnect it some how

 

[cheddar]

As far as I’m aware yes it’s fitted as standard.
It is awkward to get to, can only get at it from underneath and it’s tucked very tight above the starter motor.
If you look in the black casing where the jump-off point is near the battery, the power supply for the starter (and heater booster) connect there, you can unbolt it and see the drain stop, if so, it’s time to get busy underneath.

 

[Stussy]

Any idea which goes off to the starter & heater booster?

Thanks!

 

[cheddar]

Just follow it, it’s the one that goes through the bulkhead panel, into corrugated tubing and down to the passenger side of the engine. It’s the biggest one that isn’t going to the battery. That junction box lifts out to make things easier.

 

[Stussy]

Fixed!

Thank you very much for your help cheddar you are a legend!

If anyone who is having the same symptoms as me here is what I did-


Disconnected and Checked with ammeter each small tail in turn off the bus bar and found no significant load on any.

Then checked the main big tail that feeds busbar from battery and found a huge 30a load.

Followed cable as cheddar said and found it going to the starter motor terminal.

This cable’s crimp has 2 cables in it and sure enough the other is a very short one that connects to this horrible coolant heater!

You can’t see it from underneath the car at all (I couldn’t anyway) but I could put my hand over the starter motor and feel the plastic protector cap on the 13mm terminal nut.

I had a look from above and discovered you can JUST see the terminal of the heater, I decided I would tackle it from above so prized protected cap off with a big flat head screwdriver then got a 3/8 ratchet with some extensions a UJ and a 13mm socket.

Managed to get in and crack it off!

Unfortunately in trying to remove my socket and UJ the cables I had squeezed past with them knocked it off and now my 13mm socket and UJ live on my engine somewhere

I then got under the car to pull the crimp off the terminal stud on the heater, I needed someone else above with the big screwdriver to prize it with me pulling at same time to remove it however.

Now with the heater disconnected I did my ammeter test and found little to no load!

I then used a big bit of heat shrink
To push onto the crimp to isolate it temporarily until I think of a better more robust way of doing it.

Now the car fires up no problem even with a tiny battery I’ve had to borrow as my brand new £200 yuasa AGM is broken!

Again thank you for your help! you have saved a stranger lots of time and money with your good advice.

I really appreciate it mate

Cheers!

 

[cheddar]

No sweat, glad you are back on the road.
I normally just remove the cable from the starter and heater blind from underneath, then pull it up to the top of the engine to do the ‘modification’, not enough room for my fat hands to insulate that cable in place.

 

[Stussy]

Maybe I spoke too soon...

Car is behaving very strangely.

Left my good test battery on that evening and car was completely flat in the morning.

Checked my cctv and the cars lights where doing very strange things! Flashing and been erratic!

Obviously I hadn’t left them on I made certain I didn’t leave anything on, however they where on auto as I would usually leave them. To me this isn’t the reason.

Just hooked up yet another brand new yuasa 95ah agm battery now and struggled to get the car going as though the immobiliser has kicked in.

Managed to get it started and running to find that I had esp warning messages on the dash.

Plugged in my autel maxysis diagnosis computer to find a barrage of faults.

I’m going to put most down to low voltage driving things crazy However 2 are sticking on.

1. Heater booster short circuit to ground. (Happy with that as I want it to know it’s disconnected)

2. Rear SAM-rear signal acquisition and acutuation module circuit 54 has short circuit to positive.

Any ideas?

Thanks

 

[Stussy]

Just Googled and it points to rear vehicle control module and circuit 54 is the stop lamp

Just got out car to take a look and my brake lights appear to be stuck on!

 

[cheddar]

Oh dear.
That’s strange, last time I had one act up like that with brake lights staying on it was a water/corrosion damaged SAM unit.
Did you remember to also unplug the control plug from the heater booster, having no main battery supply and still being plugged leaves a short circuit, may have blown a fuse somewhere, but I doubt the 2 problems are connected.

 

[Stussy]

Thanks for your reply

I have ordered a replacement sam and rear control unit off eBay to try and figure it out.

Doesn’t explain the esp faults though

I left the control plug in but can soon unplug it.

Are you a mercedes mechanic/specialist garage as I’m actually local to Middlesbrough and could soon bring it over to get booked in

Cheers

 

[m80]

You're 'broken' battery has likely gone into deep discharge. More modern chargers won't 'fire up' if the voltage of the load is too low. Jump it off another battery to kick it back into life and whenh the voltage has risen the charger may well charge it again.

A DC clamp meter could be a valuable time saver for the fault finding. I've not found mine to be as accurate an AC clamp meter, and it changes reading when it's turned for opposite polarity, but for a heavy load like yours it should serve purpose
I was hoping to link the one I bought but can't find it now.

These mo mo's will throw up all sorts of faults as the voltage falls. Before replacing things I would be sure the battery is above healthy, at least 11.5 volts, and reset all codes. Many units will need normalising again, steering angle sensors for example, most will be sorted after cycling up / down, left / right, open / closed. It may be worth a battery off reset for a minute or so before doing all that.