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Michael Warfield
Michael Warfield, Factory Mercedes-Benz Technician
Category: Mercedes
Satisfied Customers: 3135
Experience:  Mercedes-Benz Master Certified technician
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2000 Mercedes S500: latch..interior lights..new battery..door locks

Resolved Question:

I have a 2000 Mercedes S500, battery went dead my neighbor hooked up an electric battery charger/starter to see if it would start. As he was moving the dial on the charger the truck latch sounded twice as if the remote was pressed to open the trunk, the interior lights became really bright and car hesitated to start but it started. I bought a new battery for it but now the door locks will not work, the trunk will not open with the remote and the battery drains completely after a couple of days. If I jump start it using a regular jump box it will stay on for a few minutes then it will cut off and will not start. I have to wait about half an hour before it will start again. It will not charge the battery, if I unplug the positive cable it reads 13.8 volts but as soon as I put the cable back on the terminal it goes down to 12.1 volts. any idea what may have happened?
Submitted: 5 years ago.
Category: Mercedes
Expert:  Michael Warfield replied 5 years ago.

Michael Warfield :

What is the battery voltage with the car running? Is that the 13.8 volts?

Customer:

The voltage is 13.8 while the car is running and the positive cable removed from the battery but once the cable is placed back on the battery post it drops to 12.1, however if I hook up the jumper cables to another car the Mercedes will stay running. If I just jump start the car and remove the jumper cables it will stay running for about 5 minutes and will turn off if I attempt to jump start it again it will crank but will not start. I have to wait half an hour to an hour before it will start again. Either way the locks and trunk will not open with the remote or the switch.

Michael Warfield :

It seems to me the alternator is just very weak and not supplying the correct amount of amperage needed.

Michael Warfield :

13.8 volts while running is ok, but I feel the amperage may not be enough

Michael Warfield :

That is why the car runs ok when you have another set of jumper cables connected.

Michael Warfield :

As for the central locking not working, the PSE pump/module that control it might have failed.

Customer:

but why is it turning off and then not wanting to start unless I wait for a while.

Michael Warfield :

I know you said you checked the fuses but the fuse for the PSE is underneath the rear seat on the passenger side behind the floor light. It is fuse number 62. I would check it and leave it pulled out for a minute or two then reinsert it. This will reset it.

Michael Warfield :

Does the engine start ok after waiting?

Michael Warfield :

without the aid of a jumper I mean.

Customer:

Also this is a brand new battery and it drained it completely after two days, the engine will start after waiting for no less than thirty minutes with the aid of a jump box or cables

Michael Warfield :

Ok, you waiting that long to jump it means the battery just gets so discharged that you have to wait for it to recover some.

Customer:

All these problems started when I made the mistake of having my neighbor hook his battery charger and using it to jump start the car, it seamed to me that he set the amps too high because the interior light became really bright and since then I have been having these issues.

Michael Warfield :

There must be a very large amperage draw on the battery when the car is shut off.

Michael Warfield :

Yes, some of those chargers fluctuate voltage between 8 and 18 volts. I have seen 15-16 volts fry control units.

Customer:

if something did burn up what would that possibly be and would that cause the battery to drain like the it is draining now

Michael Warfield :

Well its hard to say without running a test with a mercedes computer.

Michael Warfield :

Usually in my experience, and I have seen this several times, it is the rear sam module that blows

Michael Warfield :

This controls a lot of functions including all the lights for the rear and trunk latch

Michael Warfield :

Do the rear brake lights work and everythign?

Michael Warfield :

everything*

Customer:

How expensive is this module? I have not checked the rear brake lights but the front head light do work along with turn signals.

Michael Warfield :

This module is about $500 but it may not be the only one that is damaged

Michael Warfield :

It does power up all the central locking system though so it is a good chance there is a problem with it.

Customer:

when I hit the lock button on the remote the lights flash but the car does not lock

Michael Warfield :

Ok, this could mean the vacuum portion of the pump is damaged and the electrical computer that controls all of the lights is operating.

Michael Warfield :

I would have to try and communicate with this PSE pump with a computer to know for sure.

Michael Warfield :

Also, make sure you check the fuse number 62 for it.

Michael Warfield :

Did you check any of the fuses underneath the rear seat?

Customer:

Best bet would be to take it to a shop and have it looked at to be certain? I took of the back seat and did not see a fuse box.

Michael Warfield :

It is behind the light socket cover on the passenger side

Michael Warfield :

Not underneath the whole actual seat

Michael Warfield :

Just below the front of it

Michael Warfield :

But yes, your best bet would be to have all the modules tested at a shop.

Customer:

Thank you for your help I will see if I can find a mechanic here locally that can check it for me and will look for that fuse box later today to check the fuses.

Michael Warfield :

your welcome, good luck! Don't forget to click acept if i have been helpful.

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