Troubleshooting rear view mirror

[328ioc]

So I have always thought something might be up with my mirror in my car because it never seemed to auto dim very much.

Then I caught an episode of Wheeler Dealers where they bought an E39 M5 and had to replace the rear view because it had the fluid mark.

Once installed they covered the light sensor on the back of the mirror to test the auto dimming and obviously it dimmed.

I have done this with my mirror and I get no dimming at all. Is there anything else besides the sensor that can break? Or should I just replace the Mirror and be done with it?

[Oli77]

I have had the same issue since the day I purchased the car. I took the mirror apart, made sure no wires were cut or damaged (could not find anything obviously wrong). I Made sure it was not a fuse. Your mirror never lost its fluid and it looks fine?

Sorry, I am no help (but would like to find out from others).

[328ioc]

Don't worry about it, you actually did help because I forgot to mention that no my mirror has never lost its fluid as far as I can tell and it looks totally fine.

[Oli77]

Okay, we're in the same boat then.

[328ioc]

Yeah its starting to really bug me because glare really bothers me at night. Tinted windows helped a little but its still a pain.

[derbo]

Pin 3 and Pin 10 are the two power wires on the mirror itself.

If you look closely at the plug on the mirror you can see labels of the numbers on the side of the plug. Pin 3 is the power (Switch 12V Green/yellow?) and Pin 10 is ground (brown wire)


1 2 3 4 5
6 7 8 9 10



To perform an autodim test. Make sure you cover the rear photo resistor sensor. Shine a flashlight on the photoresistor sensor in the front and you should see the mirror turn green/blue. If it doesn't, make sure you have power to those pins. I tested it out with a small 12V power supply to make sure the autodimming worked before I retrofitted it in.

Double check you have power in pin 3 on the plug on the harness. You can check with a multimeter to see if it sees 12V when the key is switched on.

I don't know what else to check if it doesn't autodim besides that..

[Oli77]

Thanks for the pin info derbo. I will open the sucker up and see if I haz power there.

I tried the test with the flash light, no go for me.

[328ioc]

+1 Thanks for the info. I will try it as well.

[derbo]

hopefully it helps. I'm curious whats wrong!

[328ioc]

Been crazy busy with school, hopefully I can check it this weekend and update!

[Oli77]

Man, good luck with that plug! Its a pain, need little finger.

Unfortunately, I have 12V at pins 3 and 10. I guess I could have guessed that from the clown nose illuminating when locked.

I had 6 V between pins 1 (switch?) and 10.

[328ioc]

Man, good luck with that plug! Its a pain, need little finger.

Unfortunately, I have 12V at pins 3 and 10. I guess I could have guessed that from the clown nose illuminating when locked.

I had 6 V between pins 1 (switch?) and 10.

Sheet. My clown nose blinks as well. Maybe I don't even need to check it know and just assume its the actual mirror?

Derbo what's your opinion on this?

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[Oli77]

Maybe I don't even need to check it know and just assume its the actual mirror?

That is my conclusion at this point. Resolution: I am used to the way it is now and since I have never experienced this function and can't be missing it that much.

[derbo]

Pin 1 is suppose to have 12V when you are in reverse with the car on.

Problem with the pin outs is that it varies from car to car depending on SOS assist or not. It made retrofit autodim mirror more difficult.

[Oli77]

^ that and also, you can't test the switch (blocking forward eye and shinning on back-facing eye) cause the mirror won't switch since it is disconnected (duh).

I gave it on thinking it was a bad contact.

[derbo]

you can always drive pin 3 with 12V and pin 10 ground to test it. The clown nose is on a separate constant power source that either uses pin 8 or pin 2 for constant 12v.

[328ioc]

So I think I made a bone head move.

I thought my clown nose was lose the other day so I went to twist it back in to place and what do you know the mirror tilted to the night setting.

Do I not have an auto dim mirror or is this clown nose function a manual fail safe type deal?

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[Ryans323i]

I think from another thread, it was determined that with auto dim the clown nose will not turn.

[328ioc]

Thanks. I just saw that thread too.

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[derbo]

If you can tilt with the clown nose you do not have an autodim mirror. Auto dim mirrors have a dot at the top of the mirror


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[328ioc]

Thanks Derbo, whats the light sensor on the back (windshield side) of the mirror for then?

[johnrando]

I'm guessing the light sensor on the back picks up ambient light to see whether it's day/night. The front sensor picks up the light shining into your mirror to decided if should dim or not, IF the back sensor says it's dark.

[Oli77]

^ yep, that sounds right.

[derbo]

the front sensor (facing the windshield) is a reference light sensor. If the back sensor (one on the mirror face you look at) detects more light than the front sensor, it will dim the mirror.

[KevinC]

If your mirror is farked (as mine is on my just-purchased ZHP), you can get it fixed for $99 at radar-mirror.com. He also does custom radar detector displays, and can add Homelink to an existing mirror.

[sna77]

or just buy the new mirror with compass and homelink which is direct plug and play:
http://www.ebay.com/itm/BMW-Auto-Dim-Rear-Mirror-M3-M5-3-5-6-7-HIDDEN-COMPASS-HOMELINK-/300705478599?pt=Motors_Car_Truck_Parts_Accessories&hash=item46037177c7&vxp=mtr