W166 Heated Mirrors

SuffolkSifter

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Hi all,

I've had my 2012 W166 ML350 for around four months now and am still to figure out how the heated door mirrors work. Today was a frosty morning, I warmed up the wife's car, turned the heated mirrors on and within 5 minutes... BOOM clear mirrors. Started my ML up and no mirror heating ( -1c ), turned on the "Max Heat" button, nothing, turned on the "rear heating" and nothing. Waited for 10 minutes and zero mirror heating.

I have read that there are 3 criteria for mirror heating:

1) Rear Heater
2) Temp
3) Aircon

Also there is a sensor behind the mirror, but both failed?? I would check the fuse, but the owners manual is useless as it gives zero information. Can you purchase a workshop manual?

Any info would be great. My ML is going into Mercedes next Wednesday and will mention it to them.

Steve
 

whitenemesis

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Both my MB car's heated mirrors came on automatically at temps below 9degC
 

andy27168

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Hi,
The heated mirrors on both my MBs, a 2006 CLS 55 AMG and a 65 plate 207 convertible, are switched on/off via the CAN according to the outside air temp, and providing other conditions are met, MB's have been like this since approx. 2002-03, you're ML is almost certainly switched on/off via this method.
Earlier cars the mirrors had a ignition fed supply and a temp sensor switch on the back of the glass. (202, 210 and 129 possibly more).
If yours are not working and the outside temp is displaying correctly/accurately then in the first instance i would be checking the connections on the back of the mirror glass are clean and intact.
With the outside temp below the threshold switching voltage and the ignition on there should be 12V on the wires.
There is a WIS document detailing the temp and conditions that the mirrors heaters are activated.
If you try googling "Mercedes WIS Document GF88.79-P-1001A" it might be posted somewhere online which clarify exactly when the mirror heaters are switched on/off.
 
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Abb

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Are heated mirrors standard or are they part of some optional extra package?
 

andy27168

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My understanding heated mirrors have been standard for around 25 years, probably when electric mirrors were made standard.
 
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SuffolkSifter

SuffolkSifter

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Thanks for the info. The temp was -1c so should have worked. I also tried the rear heated screen and max heat buttons with no joy. Both are not working, which is strange. Where is the fuse for the heated mirrors located?
 

andy27168

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Hi
My understanding is there wont be a specific fuse for the heated mirrors as they are fed from the door control module, if you have no other things that are not working then it wont be a fuse issue, as stated above it will most likely the connection at the back of the glass or if you have folding mirrors a broken cable in the door mirror.
 

Major774

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My father’s 1999 E Class has auto heated mirrors, no button pressing required. It is temperature related, I don’t know what the present value is but it’s still functioning fine after all these years.

Check the back of your mirror (glass) to see if you have the 2 wires for the heated mirror function, it’s the easiest way to tell. If the wires are present then just grab some new mirrors, you don’t need to go OEM for these.
 

Diesel Benz

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Thanks for the info. The temp was -1c so should have worked. I also tried the rear heated screen and max heat buttons with no joy. Both are not working, which is strange. Where is the fuse for the heated mirrors located?

Likely a broken heating element. Quite a common problem. Not expensive to fix for the passenger side but the driver's mirror element is a bit deer if the car has dimming mirrors.
 
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SuffolkSifter

SuffolkSifter

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The car is in mercedes and both mirrors test faulty, one is £75 and the other is over £250!

How much of a job is it and can I get the mirror glass elsewhere?
 

whitenemesis

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Mercedes or a breakers/eBay. Good luck with the latter ...
 
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SuffolkSifter

SuffolkSifter

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Could I just fit two heated door mirror glasses? Or would not having something plugged into the auto dim connector on the drivers mirror cause an issue?
 

andy27168

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Not sure on the 166 but on other models the dimming and heating wires are in the same plug so the dimming wires have to be cut from the plug to be connected to the separate connection for the heating circuit.
To be honest I am doubting the diagnosis and am finding it difficult to believe they have both failed, ostensibly at the same time, I would be removing the glass and putting 12v directly to each of the mirror heaters to satisfy myself they have actually failed
Personally if it was mine I would rather have the dimming than the heating function especially as its the driver's side that the heating wouldn't be working as you could simply wipe the mirror glass with a cloth from the drivers seat.
 

andy27168

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Hi
Been thinking about this further, and I don't believe there is an activation setting in STAR to turn the mirror heaters on.
To say that simply they have both elements are blown seems rather arbitrary, especially as there are so so many cases of broken wiring in the mirror units themselves, and the fact the wiring connections are very poor for the heaters.
If you were closer to me I would offer to take a look for you.
You have made you curious now, I will plug my CLS into STAR and specifically look to see if there is anyway they can be switched on via STAR, I have explored near enough every activation/adaptation menu and I am convinced I have never seen anything pertaining to heated mirrors.
 

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