[SebC47]

Hi,

First post so please be gentle....

I have a 2013 R172, The rear screen heat and the door mirrors are not heating up. (I believe that they are on the same circuit?, although happy to be wrong about that!).

I've checked the 30A fuse in the back/boot/trunk and replaced the relay (bought from Merc), and I can hear the relay "clicking" when I turn the heat on with the button on the dash (the light on the button lights up fine).

Any pointers, wiring diagrams or suggestions are very welcome...

Thanks.

 

[Avel Du]

A gathering of heated mirrors for 172s:

Search results for query: heated mirrors

www.slkworld.com

A gathering of heated rear screen for 172s:

Search results for query: heated rear screen

www.slkworld.com

Fuses

Fuse allocation

I would be grateful if anyone can assist me with fuse allocation information for the 172. As I understand it fuses are located in the engine compartment, beside the the LH dash/glove compartment and in the boot but what is each fuse for. The manual is no help!

www.slkworld.com

Have either worked previously? Asking for a friend

 

[SebC47]

Avel Du,

Thank you for this, I will have a check of another fuse (12) having already checked 49. I'm not sure if it's worked previously as I haven't had the car long, having just swapped from a C Class, and have only just needed the rear de-frost for the first time during this recent winter weather we are currently having in the UK.

 

[DavidD]

I wonder if the rear screen issue could have anything to do with broken wires? The rear screen moves a lot when the roof goes down so there must be wiring somewhere that moves with it. Reminds me a bit of the problem with broken wires on the boot lid hinge, they give a similar problem on the rear brake light etc when they flex and break.

 

[Avel Du]

Avel Du,

Thank you for this, I will have a check of another fuse (12) having already checked 49. I'm not sure if it's worked previously as I haven't had the car long, having just swapped from a C Class, and have only just needed the rear de-frost for the first time during this recent winter weather we are currently having in the UK.

Have you got heated mirrors listed on your data card? Not all cars have it and some only have drivers mirror?
My experience is R171, not !72. Do your mirror look exactly the same?

I'll post a couple of 171 links for rear screen as might be two issues, not one.

Rear window regulator replacement

Just joined SLK World moments ago and this is my first response. I bought Mickey about three weeks ago and this is what I've done for him so far. Replaced both rear window regulators and posted How To videos on youtube. Replaced both turn signal light units in each door mirror. Restored finish...

www.slkworld.com

This is the issue David refers to methinks, but for 171:

Boot/Trunk wiring fixed

boot wiring fixed We'll that was a cold day spent outside .. but pleased with the results. First I found an old repair that had failed as they left the joint at the bend point of the wire! So I then cut the old wiring back and made new joints protected with heat-shrink and new protective...

www.slkworld.com

 

[Trev5]

Have you got heated mirrors listed on your data card? Not all cars have it and some only have drivers mirror?
My experience is R171, not !72. Do your mirror look exactly the same?

Looking at the UK MY2015 R172 Brochure, Heated Mirrors where part of the standard equipment:

But the Auto Dimming/Folding Mirrors where optional:

 

[SebC47]

Looking at the UK MY2015 R172 Brochure, Heated Mirrors where part of the standard equipment:
View attachment 623769

But the Auto Dimming/Folding Mirrors where optional:
View attachment 623770

I wonder if the rear screen issue could have anything to do with broken wires? The rear screen moves a lot when the roof goes down so there must be wiring somewhere that moves with it. Reminds me a bit of the problem with broken wires on the boot lid hinge, they give a similar problem on the rear brake light etc when they flex and break.

Thanks, I had a quick check, it all looks in really good condition, but I'll have a better look in the daylight. Great suggestion though, thank you, it didn't even occur to me to check wiring.

 

[SebC47]

Trev5, Avel Du,

I believe I have heated mirrors and rear screen heat and they are on the same circuit (hence I thought it was the fuse or relay). Very happy to be corrected.

I don't believe my mirrors are moveable, and I'm not bothered about that. I just want to see where I'm going (or rather, where I have been and what the clown behind me is up to).

Has anyone got experience is re-programming a SAM? is it a "thing"? could this resolve it?

Once again, thank you very much for your help.

 

[LeonardoDaBenz]

Like Trev said--standard.

BUT the mirrors heat up when the rear def is turned on so if one isn't working......?

Having said that, my passenger side has a code (ie not working) BUT I have no idea if the rear window def works or not (because of that fault) as I don't drive during winter months (Nov-Apr) to be able to test it.

 

[SebC47]

Like Trev said--standard.

BUT the mirrors heat up when the rear def is turned on so if one isn't working......?

Having said that, my passenger side has a code (ie not working) BUT I have no idea if the rear window def works or not (because of that fault) as I don't drive during winter months (Nov-Apr) to be able to test it.

Hi,

Thanks for replying.

Nothing is heating up. Rear view, or either mirror.

 

[LeonardoDaBenz]

Hi,

Thanks for replying.

Nothing is heating up. Rear view, or either mirror.

Are you able to run a scan to see if a code pops up? It WON"T show on the dash.

I do get a code for faulty mirror. Personally, don't care if it heats or not. It still folds and is adjustable though, just the heating element is kaput.

 

[Avel Du]

Trev5, Avel Du,

I believe I have heated mirrors and rear screen heat and they are on the same circuit (hence I thought it was the fuse or relay). Very happy to be corrected.

I don't believe my mirrors are moveable, and I'm not bothered about that. I just want to see where I'm going (or rather, where I have been and what the clown behind me is up to).

Has anyone got experience is re-programming a SAM? is it a "thing"? could this resolve it?

Once again, thank you very much for your help.

Let's shout one of the very wise wrt the above.

@VII7

 

[SebC47]

Are you able to run a scan to see if a code pops up? It WON"T show on the dash.

I have a very basic scanner, and nothing comes up.

 

[SebC47]

Let's shout one of the very wise wrt the above.

@VII7

Thanks

 

[LeonardoDaBenz]

Whilst searching, I came across several shall we say "opinions" about various MB models: some are on the same circuit, some are on different circuits, some work independently of each other, some don't, some have etc etc

So, probably best to wait till someone who knows to reply

 

[VII7]

They are not part of the same circuit.
Mirror heating is controlled by each door control module.
Typical reasons for both to not operate is breaks in the resistance film behind the glass.
Test voltage supply at plug.

 

[SebC47]

They are not part of the same circuit.
Mirror heating is controlled by each door control module.
Typical reasons for both to not operate is breaks in the resistance film behind the glass.
Test voltage supply at plug.

Thank you.

Do you mean the plug behind where the door mirror plugs into the wire (as in take the mirror off).

Would this also include the rear screen not working, or would this be a coincidence?

 

[VII7]

Note that mirror heat is activated by the rear defrost button or if the dewpoint temperature (as sensed by interior sensor) is 2C below ambient temperature (as sensed by temp sensor in front).

 

[VII7]

These appear to be separate problems.
For the rear window heat control is through the rear SAM through relay N10/2kC.

 

[SebC47]

thanks, I can assure you that our balmy British winter ensures we meet the temperature requirements for rear heated windows (so does the British summer, for that matter).

I've changed the relay C and the fuse 49 is good (tested by multimeter)