W203 Battery Change

[CMR]

Hi Folks

I know this sounds really basic, but I would really appreciate some help with this, and if you could make it as 'abc' as possible then that would be even better, perhaps it could go to the new DIY section for other C Class 203 users as I sure its going to helpful to others at some point.

I need to change my battery. Current one in vehicle has discharged and the brand new one is hopefully charged. First off, I have disconnected the battery but it doesnt pull out! There seems to be a clamp on the left hand side of the base? Does this just need loosening or what else do I need to do?

Secondly, when connecting the new (charged) battery, even though the manual says 'switch off all electrical consumers', - should I not have the headlamps (or sidelamps at least) switched on (or some other electrical comsumer? that is independant of the ignition key?) so when the negative terminal is connected (last), then there is no danger of blowing the rear SAM uinit as there is some load going through the circuit.

Many thanks for any advice

Chris

 

[television]

Hi Folks

I know this sounds really basic, but I would really appreciate some help with this, and if you could make it as 'abc' as possible then that would be even better, perhaps it could go to the new DIY section for other C Class 203 users as I sure its going to helpful to others at some point.

I need to change my battery. Current one in vehicle has discharged and the brand new one is hopefully charged. First off, I have disconnected the battery but it doesnt pull out! There seems to be a clamp on the left hand side of the base? Does this just need loosening or what else do I need to do?

Secondly, when connecting the new (charged) battery, even though the manual says 'switch off all electrical consumers', - should I not have the headlamps (or sidelamps at least) switched on (or some other electrical comsumer? that is independant of the ignition key?) so when the negative terminal is connected (last), then there is no danger of blowing the rear SAM uinit as there is some load going through the circuit.

Many thanks for any advice

Chris

Your battery has a bolt/clamp one end and it is held in place the other end by a slot in a metal bracket just slide the battery towards the fixing bolt about 15mm and it will lift out.

Yes,I would leave the headlamps on for the change on you car.

Malcolm

 

[Blobcat]

You need a 13mm socket to remove the clamp (if it is the same as the 'E') This clamp needs to be removed to remove the battery. When I changed mine I kept the car powered by connecting jump leads to another battery so I didn't lose any settings.

 

[wscheffer]

You need a 13mm socket to remove the clamp (if it is the same as the 'E') This clamp needs to be removed to remove the battery. When I changed mine I kept the car powered by connecting jump leads to another battery so I didn't lose any settings.

But, if it's dead isn't the settings already lost

 

[Rory]

I *think* details are in the cars manual (but I haven't been and looked).

A couple of things I remember seeing mentioned:
It's vital that the keys are not in the ignition when the new battery is connected or the rear SAM module will blow. Apparently they can frequently fail anyway after being powered down for a while.
The ABS etc lights may come on - turn the wheel from lock to lock a couple of times and they'll go out.
You might need to re-sync the windows (and sunroof, if fitted).

Prob not relevant to the OP if his system is dead already, but I like the idea of using the new battery to keep the system alive via jump leads, but that sounds physically awkward and you really do *not* want to short the battery terminals together.

 

[eric242340]

Malcolm, if your not too busy, this one looks like a good subject to write up for the new DIY Section. How do you think? Its a commonly asked question and an obvious DIY thing if carried out correctly.

 

[Blobcat]

But, if it's dead isn't the settings already lost

Mine at 9.8V still kept everything

 

[Blobcat]

Prob not relevant to the OP if his system is dead already, but I like the idea of using the new battery to keep the system alive via jump leads, but that sounds physically awkward and you really do *not* want to short the battery terminals together.

With a lot of MB's you have handy terminals under the bonnet that you can connect the jump leads to. You can then disconnect the battery and as long as you dont drop the +Ve lead when removing the battery you should be fine. Took less than 5 minutes for me a Cribbs Causeway carpark to change mine

 

[eric242340]

Mine at 9.8V still kept everything

Im a bit suprised at that. Normally, anything below 11.5 will cause problems with the computer.

 

[Blobcat]

Im a bit suprised at that. Normally, anything below 11.5 will cause problems with the computer.

Looking at all the issues on here I was expecting quite a few issues when my battery died. In reality everything worked it just wouldn't turn over. The thread is here

 

[eric242340]

Looking at all the issues on here I was expecting quite a few issues when my battery died. In reality everything worked it just wouldn't turn over. The thread is here

Understood and I need look no further, its a CDI, they are not as complex as their petrol counterparts. Quite sturdy on the electronics side

 

[Hibbo]

I have no experience of the fancy-dan electronics in these fancy-dan new Mercs, but I would *guess* that the computers actually run at a fair bit less than 12v, their internal power supplies providing a regulated 6 or 8v or so, so as long as the supply stays above that all will be well.

I would also have thought that a common-rail diesel is every bit as complex as a petrol, if not more. They days of fully mechanical diesel engines are long gone (thought not for me!). Besides, I think the 'settings' that people are refering to are things like display and radio things, not internal engine management settings!

 

[eric242340]

I have no experience of the fancy-dan electronics in these fancy-dan new Mercs, but I would *guess* that the computers actually run at a fair bit less than 12v, their internal power supplies providing a regulated 6 or 8v or so, so as long as the supply stays above that all will be well.

I would also have thought that a common-rail diesel is every bit as complex as a petrol, if not more. They days of fully mechanical diesel engines are long gone (thought not for me!). Besides, I think the 'settings' that people are refering to are things like display and radio things, not internal engine management settings!

I am refering to engine management problems. The CDI ECU is not as complex as the petrol versions. Its simply not as OBDII compliant in its programming. This gives it more leeway. Put simply its more versatile. And I hope I spelt that correctly. However its still hard to see how it can work so well on such a low voltage?

 

[television]

I am refering to engine management problems. The CDI ECU is not as complex as the petrol versions. Its simply not as OBDII compliant in its programming. This gives it more leeway. Put simply its more versatile. And I hope I spelt that correctly. However its still hard to see how it can work so well on such a low voltage?

I think that you are all forgetting one thing, when the engine is running,it runs on the alternator,and not the battery, you can take the battery off (not recommended ) and it will still run.

I can assure you that the ECU is equally as complex as the petrol versions,on many for a start you have to adjust the injectors and this is all nothing to do with what OBD11 does, and this just confuses the issue for non technical people.

The ECUs are designed to work on 12volt and that is that,they will work on less thats why the cars shut down consumers at 11.75 volt.

Malcolm

 

[Rory]

With a lot of MB's you have handy terminals under the bonnet that you can connect the jump leads to.

Ah - another good point that I hadn't thought of. Thanks!

(Wonder where on earth my jump leads are - haven't seen them for years!).

 

[CMR]

Hey thanks for all the replies... Basically the remote key locking has gone, and the little red flashing light on the cd player doesn't flash now so I presume this battery is pretty much discharged now.

Actually, can anyone help with this question.

When I fit the new battery, if I want to check if there is any excessive current drain, do I do this after I've connected the battery up? Do I put a meter in amp mode and then connect it up ideally without breaking any circuit? this will mean I suppose the two probes are on the one terminal for some amount of time before they can go in series when the car lead is separated from the battery pole . Is this correct? Should it be on the negative or positive (I have read conflicting data on this) side?

Thanks for any help...

Chris

 

[television]

Hey thanks for all the replies... Basically the remote key locking has gone, and the little red flashing light on the cd player doesn't flash now so I presume this battery is pretty much discharged now.

Actually, can anyone help with this question.

When I fit the new battery, if I want to check if there is any excessive current drain, do I do this after I've connected the battery up? Do I put a meter in amp mode and then connect it up ideally without breaking any circuit? this will mean I suppose the two probes are on the one terminal for some amount of time before they can go in series when the car lead is separated from the battery pole . Is this correct? Should it be on the negative or positive (I have read conflicting data on this) side?

Thanks for any help...

Chris

You will have a job to join up the new battery with an ammeter in the circuit.

This does not apply to you right now,If you wanted to trace a battery drain source then we use the banana stacking plugs and two leads from one of the terminals.
you would clamp one onto the outer clamp on the battery, then hold a probe from one of the stacked terminals onto the center of the battery post,lift the clamp off the battery then putting the other stacked lead clamp on to the battery post,

I will have to draw this out for the DIY with pics..

As at the start here, turn your headlamps on then join the battery up, you have to do it at some point.

Malcolm

 

[Blobcat]

You will have a job to join up the new battery with an ammeter in the circuit.

This does not apply to you right now,If you wanted to trace a battery drain source then we use the banana stacking plugs and two leads from one of the terminals.
you would clamp one onto the outer clamp on the battery, then hold a probe from one of the stacked terminals onto the center of the battery post,lift the clamp off the battery then putting the other stacked lead clamp on to the battery post,

I will have to draw this out for the DIY with pics..

As at the start here, turn your headlamps on then join the battery up, you have to do it at some point.

Malcolm

One note of caution is that with a lot of meters 10amp is about max before meltdown.

 

[CMR]

I think that you are all forgetting one thing, when the engine is running,it runs on the alternator,and not the battery, you can take the battery off (not recommended ) and it will still run.

Hi Malcolm

I'm a bit confused with this. I have had the 'undervoltage' come up several times now (never at the start of my journey - always towards the end of journeys although they are shortish journeys) but my point is, when the undervoltage sign flashed up last time on a wet day, the blower (climate control) didnt work at all to clear the windows, the electric windows struggled to wind down to allow some air in for me to see out of the windows, the wipers tried their best to clear the screen every now and again, the abs light was coming on and off and other lights were coming on and it was getting a bit stressful! Is this because the battery supplies current to all these items and it was obviously running out of steam, and the alternator only runs the engine? Any enlightenment greatly appreciated...

 

[television]

One note of caution is that with a lot of meters 10amp is about max before meltdown.

I forgot that bit and assume that every one has meters like mine, many do not do 10 amp, thats OK though for low level leaks, you could always add a 10Ω resistor.no I can see a little resistor all pretty colors go black No gets too complicated.

Observe what Blobcat says, I will do an article on it with photos.

malcolm