Urgently Need help with battery drain!

[dasachmo]

Hi guys,

I wonder if someone could help me with a battery issue im having for my c320. Its a 2005 facelift model w203.

3 weeks ago, the cars battery just went dead.
I drive once or twice a week so thought it may be through a lack of use, so took out the battery, charged it and put it back in. A few days later, it went dead, and I did the same. The next day it was dead so took it to Halfords who said the battery was bad and I bought a new one.

Put the new battery in and its the same problem. After 1 week the battery is dead and im down to a few days again.

I spoke to a mechanic who (over the phone ) says I need a new alternator, but this doesn't really make sense to me as the battery is going dead even when im not using the car, so I think there might be a drain.

I read about the seat control module being a common issue (although people says its the memory seats but mine doesn't have memory presets, just the electric controls.)

. I am quite novice with cars, but I managed to look under the seat and pulled out both 'molex' cables on the drivers and passenger side. (the passenger side had 3 cables). I thought this may be better so I can see if it is the seats causing the drain.

The SRS lights coming on, so I assume I took out both incorrectly. Before I mess it up any further, can anyone help!!!
One cable is blue (on both sides) and the other is white/yellow. Im not sure which to put back in or leave out?!

Please HELP!!!!

 

[markmifsud]

Now that you have triggered the SRS, your going to have to visit someone who can reset that. (mot failure) As for the drain, it could be a long drawn out task to locate it as you will need to measure each circuit for current after the car has gone to sleep.

 

[zenman63]

As above it now needs Star so you might as well get it diagnosed at the same time.
If its not charging it will not go far, like round the block and it will be flat.
Charge it and start it and look in the cluster menu for voltage or put a meter across the terminals.
Put the wires back and get the hand book out and pull fuses if needed.

 

[brucemillar]

before you start pulling the car apart, look for the simple things.

Make sure all interior lights are off, including the boot light.

Check that your alarm siren is working by leaving a window open, locking the car, then after a minute stick your hand in the open window and wave your arm about. The alarm should sound. Faulty alarms are common on the W203.

Unplug anything that is plugged into the cigarette lighter sockets.

Taking a week to drain suggests that it is a smallish drain. So maybe an ancillary being left on.

I would reconnect your seat modules first.

 

[dasachmo]

before you start pulling the car apart, look for the simple things.

Make sure all interior lights are off, including the boot light.

Check that your alarm siren is working by leaving a window open, locking the car, then after a minute stick your hand in the open window and wave your arm about. The alarm should sound. Faulty alarms are common on the W203.

Unplug anything that is plugged into the cigarette lighter sockets.

Taking a week to drain suggests that it is a smallish drain. So maybe an ancillary being left on.

I would reconnect your seat modules first.

Hi, I will reconnect the seat modules. shall I put both the cables back in or 1.

Also, the drain is maybe 2/3 days. I drove on sunday and It was dead on tuesday

 

[brucemillar]

Put it back as it was. As above to re-set the SRS you need to get it on STAR. That may highlight any issue.

To rule out the alternator? get a decent volt meter across the batter terminals. At 2.5k RPM you should +14 VDC.

 

[GLK]

In a similar situation 4 years ago, albeit in an older car, I discovered remains of a Nokia mobile/GPS system (DS-1683), but not before it munched through two Bosch S5 batteries (luckily, got the first one replaced by the second one, and the second one reconditioned and sold later, so suffered no financial loss there). I know it wasn't Bosch's fault, but I now use VARTA Silver Dynamic ones ...

 

[dasachmo]

Gonna stick the cables back in I guess. Will give it to a local garage and see if they can fix it with star. Anyone know a decent mb mechanic in East London!

 

[brucemillar]

Wright tec. Sandy Lane. Sidcup. Recommended on here. Ask for Andy the owner. Mention Bruce.

Sent from my iPhone using MBClub UK

 

[dasachmo]

just an update guys. Im thoroughly confused about whats going on

So I took the battery out of the car, charged it up to near full and put it back in on Wednesday morning.

5 mins ago I tried to start the car ( I had left the seat control module plugs out) and the SRS light was on. The car wouldn't start. The batterys gone dead again

Plugged the seat cables back in and thought I'd check the SRS light and its gone!

I guess I can rule out that the seats were causing the problem as they were disconnected so something else must be draining it. Im off to a mechanic on Saturday but wanted a few known things to look out for. A few have said its the alternator but that still doesn't make sense to me as the car hasn't been driven and the batteries gone dead while its sat on the drive for < 2 days

 

[AMGeed]

The door and seat control modules are also known to drain a battery if faulty.
Have you got Comand? If so, is that shutting down completely.

 

[dasachmo]

yeah, I uplugged the seat control modules and it still drained

I don't have a inbuilt satnav or anything like that. I've just got the standard CD slot, although there is an additional 6 cd changer that's been installed a long time ago

 

[dasachmo]

just an update, I had the car checked and have handed it in.
The mechanic put a voltmeter across the battery and it showed 14.3-14.7 v while the car was running/idling
He said it might be a faulty alternator because its overcharging.

That didn't sound right to me... any advice?

 

[brucemillar]

14.7 is not overcharging.

 

[dozypillock]

14.7 is not overcharging.

Can you not borrow an ammeter (probably at least 10 amp rated, and with an inline fuse, just in case) and connect in series with battery, with everything turned off, then see how much is being drawn?

Neil

 

[brucemillar]

Or take it to Wright Tec in Sidcup

 

[gbjeppm]

My money is on the alarm siren gone faulty.

Have you tested that it works?

If it does not work, remove fuse 8 in the boot, and see if it still goes flat.

 

[grober]

The alternator is permanently connected the battery. It contains a voltage regulator and a diode pack to rectify the AC voltage it produces to 12-14 V DC for charging the battery and running the electronics. If any of the diodes have gone short circuit they will allow the battery to discharge to earth. One way to check this would be to charge up the battery but disconnect the main charging lead to the alternator. If the discharge stops its the alternator. Any competent vehicle electrician should be able to test the alternator. Its quite possible however the leakage to earth is from another source. These can be conveniently divided into 2. The standard car wiring which can be normally be tested by disconnecting various fuses and isolating various circuits. The second much more problematic is any non standard aftermarket equipment which may have been piggybacked on to the cars system in a non standard manner. Your best bet is to get it on a Star system as suggested.

 

[AMGBlack]

The alternator is permanently connected the battery. It contains a voltage regulator and a diode pack to rectify the AC voltage it produces to 12-14 V DC for charging the battery and running the electronics. If any of the diodes have gone short circuit they will allow the battery to discharge to earth. One way to check this would be to charge up the battery but disconnect the main charging lead to the alternator. If the discharge stops its the alternator. Any competent vehicle electrician should be able to test the alternator. Its quite possible however the leakage to earth is from another source. These can be conveniently divided into 2. The standard car wiring which can be normally be tested by disconnecting various fuses and isolating various circuits. The second much more problematic is any non standard aftermarket equipment which may have been piggybacked on to the cars system in a non standard manner. Your best bet is to get it on a Star system as suggested.

Grober is quite correct. A diode that has gone short circuit can allow a path to earth to drain the battery (disconnect it like he says and you can rule that one out). Sometimes even putting your hand on the back of the diode pack (if its warm after the engine is cold) then thats a tell tell sign it could be at fault. Another common leakage issue could be the starter motor solenoid / system (as this is directly connected to the battery) or (and this is the worse one) a chaffed wife somewhere. A whole manner of issues could be at fault with a leakage like this. Remember it can only be systems which have a permanent live connection.

Can you clarify if you put the charged battery back on and the car starts okay, and does later in the same day etc. A poor earth connection from the engine body to the battery can give you the impression of a flat battery if it is loose or damaged etc. If it is sluggish even with a fully charged battery I might want to check this. Since you have changed the battery it rules out sulphated or damaged plates in the battery.

If this is not the case and the car starts okay for a few days, then we are looking at a drain for sure. My suggestion would be to (as painful as it sounds) to take it to a Mercedes Dealer to check it. You have already invested in a new battery which most likely wasn't needed and you could be a few hundred pounds out of your pocket before you even get an idea whats wrong. Money well invested in getting a proper diagnostic done on the car. My dealership won't charge me if they can't fix or find a fault, maybe I am lucky.

if I was near, I would disconnect the earth lead and plonk my Ammeter inline and measure the leakage and then start to disconnect items (carefully, starting with the Alternator, then starter motor, Alarm etc.) Whatever you do, don't leave a disconnected +ve dangling as if it touches the bodywork you might have more than a flat battery to contend with. If you notice a sudden drop in current, then that could point to the offending issue.

Sorry can't be more help and good luck.

 

[dasachmo]

Hi guys.

Just an update again, could really do with some help here!

So it went dead last Thursday, annoying. So I called up my local garage, took the battery out and charged it overnight.
Managed to take the car in on Saturday morning. It obviously started fine and left it with the mechanic.

He tested it when it was on as I previously said, 14.3-7 V which appears normal as you have said before.

Just my luck, Monday morning he tried it and it started first time, same thing on Tuesday and today!. He said its started first time and cant find anything wrong.

Ive taken the car home and he said theres no issues he could find.

I have a ammeter, so I did just as you guys said - excuse me because im not proficient in electrics.

Firstly, I put the machine on the + and - of the battery when the car was off - The reading was 12.3 V

I disconnected the +ve, touched the +ve to the ammeter and other lead to the +ve at the battery. The reading fluctuates between 1.3-1.5 Amps.

I disconnected the number 8 Fuse and tried again and for some reason it went up to 1.7 Amps which was confusing.

Put everything back together. Opened the drivers side window and locked the car. The alarm tow light flashes, im not sure if that's normal or not, I really don't remember from before. I stick my hand in and nothing happens.

I open the door from inside and the hazard / indicator lights flash repeatedly but no alarm sound.

Need to try again which I will in a minute because reading the manual it says wait 15 seconds for the system to arm before you do anything .

What do you guys think? is 1.5 amps normal?

Also, I'd love to take it to wright tec but im quite north east London and its a bit of distance. That being said, I may just have to if it goes dead again.

I didn't want to start pulling fuses in case something wipes or I get a SRS fault or something.