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· Registered
2 Posts
Discussion Starter · #1 ·
Hi all,

I have a w209 2003 CLK 320. And it's completely dead (electrically). Can you offer me advice?

Recent history:

* Alternator replaced
* I bought a new battery (before the above change)
- I have the wrong, 70Ah battery (a website told me otherwise)
- It's a VARTA Black Dynamic sealed battery
* I had a hell of a time with the Garage that did a good job on the alternator
- They broke the bonnet release catch under dash. Didn't tell me of course!!!
- First attempt at repair resorted in electronics going wild (no wipers for e.g)

* The other day I couldn't unlock it electrically
- I crawled through boot due to seized door lock!
* After restarting car, with a key reprogramming 'to-do' It's now dead
- I.e. I guess the problem wasn't the locks.
* Battery was at 1.2v with a multimeter tonight

Possible sources of this error/ to-do
* I'm charging the battery now
- New charger...keeps resetting...could the battery be toast?
- Would an alternator expecting a 90Ah battery have been overcharging?
* Plan to get a charged battery in there and test circuits for a power drain
- Could the garage have botched the re-repair of bonnet catch job
- Might this be stopping the car going into standby, causing drain?
- How on earth would I test for this?
* Area under batter was damp. Possible other explanations?
* Maybe I should buy a 90Ah battery?

I really appreciate your help



· Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
25,443 Posts
It sounds like you definitely have a battery/alternator problem. Using a lower amperage battery with a higher amp alternator wouldn't be a problem. Lead acid batteries aren't susceptible to overcharging that way. As long as the alternator voltage output is good (12.5v -14.5v) then the battery should be fine. Battery amperage is really just related to cold cranking amps, and yes, MBZ's need a lot because of all the extra electronics that need voltage, too.

I suspect you have some damaged electronics due to the low voltage. You might have blown a SAM, and even a defunct key. If you get a voltage drop at just the "wrong" time when starting the vehicle, the key's rolling code can become desynchronized with the rolling code the vehicle expects. When this happens, the key is basically dead - you'll need to have it replaced. I'd get a good battery, start the vehicle, and then start checking the alternator.

· Registered
2 Posts
Discussion Starter · #3 ·

Sorry for the delayed reply. I have now:

* Charged the battery. It held charge
* Refitted it in Car. Started engine and get 14+ volts across terminals

However I have 3 malfunctions showing relating to 'failed lights' and substitutes.

Plan is:

* Check all the fuses/bulbs
* Monitor the voltage, not using car.

These SAMs sound like a real pain!

· Premium Member
2004 CLK 240 Coupe
11,408 Posts
Hi Andy - would you please fill in your profile with the UserCP at the top of the page ^^^ showing us your model/year/location, as this can help with replies.

'Failed lights' I understand. But what are 'substitutes'? :confused:
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