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Registered
1989 300 SE & 1999 C280
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5 Posts
Discussion Starter · #1 ·
Yesterday my smart key did not unlock my doors or allow me to turn the ignition. Naturally, I thought it was a smart key battery issue so I changed the batteries and had no luck. I have since learned that the smart key should still allow the car to start even if the batteries in the key are are bad.

I have multiple questions here:

1) If the car's battery is dead, which for whatever reason, I believe it is as the dome light does not turn on; what is the nature of how the smart key behaves? Shouldn't the smart key still at least allow me to turn the ignition or no?

2) If the battery is dead then should you still hear the "grinding" noise when you place the smart key in the ignition? Or not?

3) Is it possible by replacing the car battery my problems may be solved? Presumably it depends on answers to #2

3) Which fuse number should I check to see if that is an issue?

4) My car is parked on an incline (uphill) with the wheels turned to the left and I read where others have had an issue with the smart key in this situation?

Thanks so much for any ideas!!!
 

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Registered
1922 Ford T no OBD, no ECU, no SCN
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37,842 Posts
Smart IGNITION key doesn't have the battery. It is only the door remote attached to some of them that does.
Assuming your C is the same generation as mine E -everything in it is electric. Meaning bad car battery and nothing will work with the exception of mechanical lock in single door.
 

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Premium Member
2001 E320 - Brilliant Silver/Ash: 107,000+
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17,193 Posts
Unless it is a fairly new battery (in which case you might be able to recharge it) I would start with replacing the battery. Call MB roadside assist and they will do it for no labor charge, or at least they used to. Or if you are a DIY, you can get a Costco battery for less money.
 

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1989 300 SE & 1999 C280
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5 Posts
Discussion Starter · #4 ·
Problem Solved....Glad it was Saturday and had time to deal with this. Key (no pun intended) is to try not to panic...Steps:

1) Walked down to a local shop and borrowed a battery charger
2) Hooked up to battery, turned it on
3) Unlocked the door using the mechanical key
4) Alarm immediately went off so I immediately knew the battery was the issue
5) Turned off alarm via panic button
6) Started car & unhooked the battery charger
7) Drove to repair shop and had them test the health of the battery before spending $140.00 on a new one
8) Drove the car for about 45 minutes so the alternator could re-charge the battery
 

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Premium Member
2004 CLK 240 Coupe
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11,385 Posts
Well done - you did all the right things - in the right order! :)

Btw, that 'grinding noise' you referred to when inserting the key, is the pin of the steering lock being withdrawn following a successful data exchange between the key and the EIS module. Only then can the key be turned further to start the car. You will never get that 'labored' start of yesteryear from a low battery with your MB. If your battery is low, the start is not enabled.
 
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