C220 cdi starter fuse blows

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pugilist

Member
Joined
Feb 8, 2010
Messages
42
Location
Born in a city moved to the country side.
Car
C320 CDI Sport
My earlier post describes problems as a result of a flat battery. Have just bought a new battery and the car started great first time. Have run the car and switched it off twice.
On trying to restart again the 20amp fuse for the start circuit blew. Replaced the fuse and it blew immediately again. The starter circuit has blown this fuse a number of times during the past few months. Now it appears to be permanent. It blows straight away. Any ideas anybody?

Also is it ok to tow the car as it is automatic and may need to get it to my local indie. I am not used to autos so a little advice on this would be useful too.

Thanks all.
 
I know I need to release the gearbox from park by pressing the lever hidden in the tray behind the gear selector. Once the car is in neutral is it ok to tow the car? If so, is there a restriction on how far the car should be towed?
 
Not got my cars user manual in front of me but it has towing advice in there so yours should have too. IIRC it has to be a suspended tow so the driven wheels are off the ground.
 
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My earlier post describes problems as a result of a flat battery. Have just bought a new battery and the car started great first time. Have run the car and switched it off twice.
On trying to restart again the 20amp fuse for the start circuit blew. Replaced the fuse and it blew immediately again. The starter circuit has blown this fuse a number of times during the past few months. Now it appears to be permanent. It blows straight away. Any ideas anybody?

Also is it ok to tow the car as it is automatic and may need to get it to my local indie. I am not used to autos so a little advice on this would be useful too.

Thanks all.

Friend, try an 25 AMp fuse.

Originally, it comes with 10 or 15 Amp rating. Then, as it gets older, it starts to require more current, and you can put in up to 25 Amp fuses. More than that will need starter replacement/repair. If the 25 Amp fuse works, then you're good for another couple of years.

So the guys at MB told me.
 
I am not near my car at the moment, but I remember that there is a button on the right of the gear leaver which you need to press if you want to have the car towed.
 
Hi Jobela,
Thank you for taking the time to respond to my question/problem.
I cannot understand why the starter would require more current to start as it ages. I have never know this before in any car. Putting the fuse rating higher will stress the cables further in the starter circuit and could potentially cause a fire, depending on the rating of the cables. It could also have the effect of burning out the motor I would have thought.
If the motor does require more current then I would suspect a mechanical problem that may be causing the motor shaft to sieze or the bearings starting to fail. Perhaps I should get the starter motor out and check it mechanically.
Thanks once again for the information and your suggestion possibly hints to a mechanical fault. I will definately try the 25 amp fuse to get the car started though.
 
Hi Jobela,
Thank you for taking the time to respond to my question/problem.
I cannot understand why the starter would require more current to start as it ages. I have never know this before in any car. Putting the fuse rating higher will stress the cables further in the starter circuit and could potentially cause a fire, depending on the rating of the cables. It could also have the effect of burning out the motor I would have thought.
If the motor does require more current then I would suspect a mechanical problem that may be causing the motor shaft to sieze or the bearings starting to fail. Perhaps I should get the starter motor out and check it mechanically.
Thanks once again for the information and your suggestion possibly hints to a mechanical fault. I will definately try the 25 amp fuse to get the car started though.

Ask an MB dealer, they will tell you your starter is fuse rated from 10 to 25 AMP. When the 25 AMP fuse blows, it's time for an overhaul on the starter or a new one, or a rebuild one.

I've seen it.

Best of luck.
 
Hi Jobela,
Thank you for taking the time to respond to my question/problem.
I cannot understand why the starter would require more current to start as it ages. I have never know this before in any car. Putting the fuse rating higher will stress the cables further in the starter circuit and could potentially cause a fire, depending on the rating of the cables. It could also have the effect of burning out the motor I would have thought.
If the motor does require more current then I would suspect a mechanical problem that may be causing the motor shaft to sieze or the bearings starting to fail. Perhaps I should get the starter motor out and check it mechanically.
Thanks once again for the information and your suggestion possibly hints to a mechanical fault. I will definately try the 25 amp fuse to get the car started though.

Note that it is not the actual starter motor fuse, 10 or 25 amps would be far less than the actual starter motor draws.

This is the current of the drive circuit to the starter motor solenoid, isn't it. I've seen this same advice to increase the fuse size for some other MB models with a similar starter circuit approach.
 
Hi guys,
Well the car has been with my indie today and they are top notch. However, they have so far found nothing wrong with the car. They have started it about 30 times during the day and not a single problem. He is keeping it until tomorrow and will try again. They have also checked all the wiring and connections of the starter circuit and no fault found. They said that if I wanted they would run the diagnostics but they said it won't show if the problem is with the starter. So probably not worth the £45 to connect it in.
So it looks like replacing the 20 amp fuse with a 25 amp fuse is the next stage and see how it goes from there I guess. Therefore I bow to your superior knowledge about this problem. Thanks to you for your advise on this and I will let you know how it goes.

(The current generated in the circuit is a result of the starter motor engaging with the fly wheel and then has to overcome the inertia of turning the engine. The solenoid is simply a fast acting switch that handles high current).

Thanks again, have a great weekend.
 
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The nightmare continues with this car. My local indie has had the car for 2 weeks now! The starter motor has been replaced. However the battery discharges and is flat in a week. The indie are checking all the circuits 3 at a time. Each morning they go back and check the voltage drop. It continues drain. They have been disconnecting circuits for a week and still the battery drains. Has anybody else had this problem or have any ideas as to what this problem may be?

Regards.
 
The nightmare continues with this car. My local indie has had the car for 2 weeks now! The starter motor has been replaced. However the battery discharges and is flat in a week. The indie are checking all the circuits 3 at a time. Each morning they go back and check the voltage drop. It continues drain. They have been disconnecting circuits for a week and still the battery drains. Has anybody else had this problem or have any ideas as to what this problem may be?

Regards.

Odd if the workshop has pulled fuses but not measured the current drain untill they identify a fuse that makes the (excess) drain stop. They might have ended up finding the memory seat module being the issue, as suggested above.

Do you think this shop can do their job well? If any of the workshops known from this forum were nearby, I would reconsider which workshop to use. Or you could do it yourself.
 
Thanks for the responses guys. Diesel Benz am sorry but I cannot really understand what you mean. I have read other posts and a couple have suggested the seat modules also. Thanks for that.
I put the car in the MB dealership in Cambridge on Monday morning. They called me in the afternoon and said that the battery was at fault. I explained to the guy that I suspected the battery initially and I replaced the battery with a new item. However the problem continued. He continued that the the battery was at fault and it needs to be taken back and replaced or they could replace for £145. We took the battery back and it was tested by the supplier. They said the battery was fine! I returned the battery to the dealership this morning and explained the battery was ok.
Today they have been disconnecting circuits and they called to say that the current drain was apparant until they disconnected the front SAM unit, I asked what this was and the guy was not able to tell me!! (MB Dealership!!!). He then told me that they reconnected the SAM unit and the problem had gone. They checked a few more times and the problem had not re-appeared. They are going to check again in the morning.
This car has been a complete nightmare. Now the fault has amazingly disappeared and so we are no better off at the moment (other than it will actually work like a car again, but for how long?) and it has cost me many hundreds of pounds.
So SAM unit anybody?
 
Don't want to spoil your joy, but you write that "the fault has amazingly disappeared". The reason for that could be that by removing the battery, the fault register in the onboard computer is cleared (i.e. computer reset).
I had electrical problems in my car and was clearing them by disconnecting the battery. It took a while to discover the real cause.
 
Hi m7m, not sure that there is any joy in owning a merc! The problem with the car is not a fault register, the battery drains. The battery has been disconnected many times since this fault has been apparant and it does not clear the fault. It was the action of disconnecting the front SAM unit, whatever that is, that supposed to have cleared the fault.
Anyway I dropped into the dealership today and asked how they were getting on. The guy dissappeared into the workshop and after a long time returned to tell me that it was the drivers seat module that was causing the battery drain. So after previously telling me the fault had gone afer disconnecting the SAM unit it is now the seat module. They will replace it tomorrow and hand me a bill for over £400. They better be right!
 
Hi m7m, not sure that there is any joy in owning a merc! The problem with the car is not a fault register, the battery drains. The battery has been disconnected many times since this fault has been apparant and it does not clear the fault. It was the action of disconnecting the front SAM unit, whatever that is, that supposed to have cleared the fault.
Anyway I dropped into the dealership today and asked how they were getting on. The guy dissappeared into the workshop and after a long time returned to tell me that it was the drivers seat module that was causing the battery drain. So after previously telling me the fault had gone afer disconnecting the SAM unit it is now the seat module. They will replace it tomorrow and hand me a bill for over £400. They better be right!

The front SAM is basically the fuse and relay box at the front of the car. I did not check which fusebox feeds the seat control module but if they detached the whole SAM, it could well have disconnected power to the faulty seat control module and the quiescent current obviously too.

I did not count how many times the seat control module was mentioned in this thread alone but it is a very common issue and it was mentioned in this thread too.

If the SAM itself was OK (no bad solder joints or short circuits), they should have figured out a drop in quiescent current when they were first time pulling fuses from the car. This is what I "complained" previously about your workshop. The standard procedure to find ghost current consumers at home is to measure the current draw from the battery when ignition is switched off and the car is supposed to be in sleep. If the current consumption is higher than the rated figure (typically in the range from 40 to 80 mA), one can pull of fuses from potential current consumers one by one. If the current drops after pulling a specific fuse, you get an idea of the faulty part.

Sometimes identification may not be straightforward if the current consumption comes from a CAN bus that is kept alive but at least a group of guilty parts has been identified.

This is something I suggested you would have done yourself. Having done that and replacing the seat control unit would likely have been less than £400 and you would probably have saved a lot of your time by doing it yourself.
 
I get your drift Diesel Benz and the 'workshop' you mentioned did the things you mentioned, I think!
Unfortunately I am a very busy guy and I just don't have the time to be working on my daughters car. So £485 later the car now works. Hopefully for a few weeks anyway. If the advice had come sooner I would have worked it over the weekend but hey.
As the advert says: 'Joy is BMW'
 
Does your car have that second battery beneath the aircon filter (I think)? Could be that...
 

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