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The battery is draining. And the alarm is going off by

Customer Question
The battery is draining...

The battery is draining. And the alarm is going off by itself. Like the lights atleast. I think my siren no longer works. I do not hear it.

Mechanic's Assistant: Have you tried locking and unlocking the driver's side door using the key itself?

In order to do what?

Mechanic's Assistant: What is the model/year of your Mercedes?

2000 s430

Mechanic's Assistant: Are you fixing your S430 yourself? What have you tried so far?

Yes. I am metering the battery to see what fuses stop the draining of power And I have tried not arming the alarm, so that it wont go off. I think not arming it keeps it from no longer going off, as its not armed. But sometimes it arms itslef

Submitted: 5 months ago.Category: Mercedes
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Answered in 2 hours by:
12/11/2017
Mercedes Mechanic: Matt, Engineer replied 5 months ago
Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 23,075
Experience: Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello and welcome to Just Answer

the alarm will go off if the battery voltage drops below 10V, so I wouldn't worry too much about that aspect

solve the battery drain and the security system should then be OK

I'd first check the easy things like is the boot light or any other interior light staying on then check that the main battery connections are tight and in good condition also check the earth strap to the engine /gearbox.
Next I'd check the current drain aspect, the best way to find what circuit is causing the excessive currant drain is to fit a current sensing multimeter in series with the positive battery lead on the car and the battery, or use a current clamp meter on the battery positive cable.

A typical current drain with everything off and un-alarmed should be around 0.05Amp and if its higher than this remove a fuse and re-measure, if measurement doesn't change then replace the fuse and remove the next.

Once you've isolated the circuit with the excessive drain check the wiring connections and plugs to components and the wiring harness that runs by the engine bay fuse box - the wiring harness chaffs / rubs through and gets damaged - but its not always easy to see so be careful when checking..

Also check that the alternator is actually charging the battery in the car by taking a battery voltage reading with the engine off then another with the engine running. The 2nd reading should be higher than the 1st and climbing steadily. And also check that the alternator is secure to the engine as this provides the ground for the charging circuit and make sure that the engine / gearbox earth strap is secure and the contacts are clean and bright.

if the alternator appears not to be working - take it to a electrical specialist and ask them to test it as sometimes you can replace just the diode pack and this will repair the alternator without requiring replacement

And one last thing is – how old is the battery? – As even good quality ones need replacing every 5 years and faulty battery just won’t hold a charge

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Customer reply replied 5 months ago
Hello, thank you for your help. I understand you did not have anything to do with how the service was sold to me.
Its was very scammy. The pop up window indicated it would be only $5 to speak with you. And through some clever wording made it seem this would be the price, but then my paypal was charged for $31. I just do not do business that way. So I will be asking for a refund. Consequently, I am a mechanic, and I have tried all you have suggested already. Thank You for the advice. I believe I am going to replace the siren, and go from there. Thanks,
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