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Discussion Starter #1
Hi!
I am quite new here, and I hope somebody can help me. I got a 2003 e270cdi, and the problem is the red battery light keeps coming on after rain or carwash.
This problem drives me crazy.
Maybe somebody had this problem.

Many thanks.
Tibor
 

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Discussion Starter #3
Thank you, I have checked, seems to be alright, tight and clean.
I think there is somewhere a water leak

Tibor.
 

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'71 Pinto
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4,515 Posts
I think there is somewhere a water leak
Check spare tire well for leaks/corrosion (main battery, battery control module, rear pre-fuse box location), water collector wiper area drainage (auxiliary battery, battery relay location), passenger footwell (front pre-fuse location) and of course interior fuse panel at side instrument panel, front SAM (rear left engine compartment), and rear SAM (left trunk interior at wheel well)
 

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Discussion Starter #5
Thanks, for the reply, I will do it soon. The spare wheel area nice and clean.
I think it is a drainage problem somewhere on the front.

Thanks.
 

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2004 E320 4Matic
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45 Posts
If you are getting the red battery warning light on your cluster it's linked to your aux starter battery which is located in the front left of the engine bay under your exterior cabin filter. You can test it to see if it's holding 12v.

If your main battery was going in the rear trunk it would give you a battery protection warning and you would temporary lose convn functions like heated seats, etc...

If you haven't replaced the aux battery it's probably about time if your car is an 03.

As for why it comes on only after rain or car wash its a bit of a toss up but worth checking out and doesn't need to be done at a dealer as it can easily be replaced but the battery size is odd and has to be oem.
 

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Discussion Starter #7
Hi!

Thanks for the reply.

The main battery is brand new Mercedes battery. The small one is a Bosch AGM (sealed) battery wich is about 1 year old. I bought the car with that.
So maybe the computer "complains" about the small battery, maybe it has different characteristic.
I think the previous owner fitted this cheaper one just before selling the car.
Can it cause the problem?

Thanks
Tibor.
 

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Super Moderator
99 ML430, 00 ML320, 05 E500 4matic Wagon
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22,145 Posts
You do not have to pay the dealer over $200 for an OEM aux battery.
If you are in the UK then a motorbike shop can get the Yuasa battery in that size for at
least half the price.
 

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2004 E320 4Matic
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45 Posts
If both batteries are in good fair condition to your knowledge you may want to try and unplug your bcm module as sometimes it doesn't clear properly and something maybe stored internally cause the light to come out. It's a small black box connected to the negative battery terminal that's located where the spare tire is mounted to the outter side of the trunk. Just unplug the wire and let t sit for 10 mins and plug it in and go for a car wash and see what happens.

Hope it helps!
 

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Discussion Starter #10
Hi, thanks for the reply.

It is weird, because last night was a very heavy rain, but in the morning NO red light. Anyway I will do it, just to clear the stored faults.

Thank you.
Tibor
 
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