DIY: Auto-dimming mirror & CH/LH retrofit (picture heavy)

[maccalo]

Writeup for retrofitting auto-dimming rear view mirror and coming home/leaving home function to any A4 B6 with highline equipment.

This retrofit requires some knowledge of car electrics, and a registered version of VCDS lite.

How do I know if my car is highline?
If you have bulb out warning - you have highline
If your CECM part# is 8E0 907 279 E or F - you have highline

NB! You need CECM 8E0 907 279 F, which is the only CECM supporting AUTO lights and CH/LH function.

I did not do the auto dimming wing mirrors, hence it's not a part of this DIY.

Disclaimer: I am not a mechanic, and will not take responsibility for anything that may be damaged or broken while using this DIY on your own vehicle. This DIY is intended as a guide only.

Prerequisites

Parts

• CECM (Central electrics control module) - paid $37
  8E0 907 279 F (always installed in S4)
• Auto-dimming rear view mirror w/ light sensor - paid $50
  8E0 857 511 (Gentex 015621)
• Headlight switch w/ AUTO position - paid $16
  8E0 941 531 B
• CH/LH switch - paid $25
  8E1 919 094 B (LHD, for cars with xenon)

Wiring

• Plug for CH/LH switch (8 pin) - paid $10
  8Z0 972 883
• Plug for auto-dimming mirror (6 pin) - paid $10
  4B0 971 833
• Wires 20-22 AWG, 3 metres - paid $15
  White, black, grey, green
• Cloth tape for OEM appearance - paid $3
  For OEM appearance of harness
• Audi repair pins - paid $10 for 10 pcs
  000 979 018 E

Let's get started

DISCONNECT YOUR NEGATIVE BATTERY TERMINAL.


Remove interior dome light cover (just pulls out)


The second plastic cover also just pulls out (has 4 plastic clips on it)


Remove two philips screws to remove the base of the panel


Then you can pull the base downwards to remove it


Locate this plug, and remove it (two wires to be inserted here later)


Remove the sun blind on the drivers side, by pulling out this cover and unscrew the T25 bolt behind it


You also need to remove this handle to loosen the A-pillar trim (Torx 25)


Loosen the A-pillar trim by unclipping the 3 clips along the A-pillar (note: my new wiring is shown here, not yet zip tied)


Pull out your old headlight switch by pushing, turning clockwise and then pulling outwards.


Remove the plug. Note: this is also a way to check if your car is highline - high gauge wires indicating highline, low gauge (thick wires) indicating lowline (lights are then operated by switch, not CECM).


This cover pulls straight out


Remove drivers kick panel - 3x 8mm hex bolts, first one located as shown on picture, last 2 located above the pedals (one on each side)


Unscrew and unclip the fuse panel and pull it downwards to expose the CECM.


Unclip all 3 plugs on the CECM and locate the 32-pin grey connector - it should look like this


Remove the purple lock, and pull out the white center frame

[maccalo]

The fun part: Wiring

I've been searching the web, and found several good writeups, both in English and German. Based on the information I found, I have made a new wiring diagram in English, with all the correct part numbers and pin outs:

Feel free to use this!


Wire harness in the making


Finished harness. It measures approx 2,5 metres from mirror end to CECM end. I used the cloth tape as pictured above to make it look OEM.


This pictures shows the mirror connector and the loop that goes via the interior dome light connector.


Remove the platic cover from the 12-pin dome light connector, by unclipping it from the right end of the connector as it's shown in this picture.


This connector already had two unused pins! Insert your wire from pin #6 on the mirror end, in pin #1 on the plug. In pin #11, insert the wire running to pin #19 on the CECM.


Zip tie the wiring harness along the existing wires in the A-pillar, and make sure it doesn't get in the way of your airbag.


3 pins to be inserted into the headlight switch connector. The 2 blue wires inserts into pin #7 and #16 (these are also open). The black wire should replace the wire in pin #1 (remember: this black wire is connected with pin #1 on the mirror, pin #4 and #8 on the CH/LH switch and runs to pin #18 on the CECM). Make sure to insulate the old wire from pin #1 and tuck it away.


Insert the 5 pins into the 32-pin connector on the CECM. All these slots are open, which means no tapping into wires!


Connect your ground wires to the grounding point behind the instrument cluster. If you copy my harness design, you should have plenty of length to reach this spot.

Installing the mirror


The old mirror pops off with a slight pull against you from one side. When it does, the base is still attached to the windshield. To remove this, get a firm grip around it and twist counter clockwise. No tools needed in my case!


This is how the B6 mirror base looks like when removed. I forgot to take pictures of the windshield base whilist installing the new mirror!


Place your new mirror against the windshield base with the wiring extension end pointing in a 10 o'clock direction. Push slightly against the windshield, so that the hooks are engaging, and turn clockwise until it clicks in place. Connect the harness and install the wiring cover trim.


How it looks like from the outside

VCDS coding


Enter 09-Cent. Elect. to recode the CECM module


Follow the instructions given in this picture.

By now, your car should have a working auto-dimming rear view mirror, coming home/leaving home lights activated at dusk/night time, and auto lights if you're coded for the proper region.

My total cost for this project was approx $175 (excl. shipping).

Thanks for looking

(Also posted on others forums - let me know if I should remove it from AZ)

[k909068]

This is awesome, thx for the write-up!!!

[Maliaudi]

Hello and thank you for the guide, this was a retrofit that i would like to do for a long time and thanks to you now i do that and everything works perfectly! Thank you very much, only one thing i want to ask you, the coming leaving home works with the switch set to AUTO and also with the switch set to 0, si that normal?

[Osher67]

Wow this is really helpful I'm trying to piece mine together.
I replaced my headliner harness with a auto dimming coming home harness.

[ohecht]

Hello. I've been trying to get this to work and have an issue with the light sensor throwing an error so the headlights are always on when the switch is in the Auto setting. The car is a 2005 Audi A4 B6 that already had the "high line" light switch and CECM. The wiring harness for the mirror was also already in the headliner just not connected. I'd previously retrofitted an auto-dimming mirror with compass and used that existing harness and connecting some power and ground wires at the kick panel. My mirror is the type without the power switch, but it does have light sensors on the front and back...I assume the front-facing sensor is the light sensor that should work for the Auto headlights. For this project, I've added the CH switch and a headlight switch with the Auto setting. Everything else works fine...the Auto setting on the headlight switch just has the lights on all the time.

I followed the wiring diagram exactly (at first) and disconnected my existing connections to the mirror. Most of the connections in the diagram were already present in my car and I was able to connect to them where they seemed to dead-end at the kick panel. I think this was expected as my car seems to be wired for the Auto lights and mirror but I assume the factory left out some connections or a harness at the kick panel since they weren't installed options on my particular car. Anyway, the first issue was that the mirror that had power before no longer had power (remember I'd disconnected the power I'd previously used for the mirror to match the diagram in this post exactly. I'd get a light sensor error on the dash whenever the light switch was in the Auto setting. Since I think the light sensor was in the mirror and had no power, I assumed that getting 12v into that circuit would solve the problem (it seemed like following the diagram exactly as in this post had no power in the circuit connecting the two Pin 1s on the headlight switch and mirror, Pins 4 and 8 on the CH switch, and Pin 18 on the CECM). I reconnected 12v to that circuit and the mirror powered up again...I assumed that would also give the light sensor power and allow the Auto setting to work. I have the same issue, though. I reverified all the circuits and they're all showing continuity between the right points and power and ground where they should be. The light sensor(s) on the mirror seem to work, too...the compass display will dim if I cover the sensor for a few seconds.

In VCDS, the DTC that's always there is "02104 - Light Detection Sensor (G399) 30-10 - Open or Short to Plus - Intermittent" - that one will come right back as soon as I clear it. Another code, "02105 - Supply Voltage for Light Detection Sensor 57-00 Electric Circuit Failure" shows up occasionally but seems to clear and stay cleared at least until I made changes to test things in the circuits. And I did of course code the car to think it has the light sensor. The light sensor status is always showing "on" in VCDS.

Thanks in advance for any ideas anyone might have...I really thought getting power to the mirror would solve this issue.

Olivier

[ohecht]

So I tried the other style of rear view mirror (with the power button) in case the one I was using didn’t have a light sensor. I thought it worked at first...the same power code supply voltage (02105) comes back on but it now takes a minute or so to throw the code each time I select the Auto position on the headlight switch.

[Osher67]

How many wires do you have coming from your mirror?
I haven't brushed up on this in a while mine is all wired up and I never coded and tested it yet.
It sounds like you might be missing some wires for the rain sensor you can see if your mirror has it on the back side little white thing.
But I went to a junkyard and tore apart wires to triple confirm all of the colors and places.

Got a headliner wire harness and all wires and pins I needed but to just do rain sensor it sounds like you might be missing some wires for communication.
Sorry I don't have much to add at the moment I did this a while back fitted auto dim mirror and side mirrors, auto headlights, ch/lh and drl, along with Homelink all oem wires and pins/ harness from other cars.

I'll try to check it some when I'm back next week.

[ohecht]

Hi Josh. I have four wires coming from the mirror leading into a six-wire connector that was unused before but already in the car. The mirror does have the little sensor pointed through the glass from the backside of the mount and it did work flawlessly for an entire drive last week so it can’t be a completely missing connection or component. Something more transient is happening.

That said, 95+% of the time I get the sensor error. The only other possibly related symptom is that the rear fog light bulb warning also occurs about half the time, even though the bulb is working fine...it’s still an incandescent bulb and I’ve tried multiple bulbs. This happened before I did anything related to the mirror or auto light switch but happens more frequently since this project.

Does anyone know of an issue with either the light switch or the CECM that might results in one or both of these issues?

I’m sure the wiring is all correct per the diagram here and I’ve confirmed the continuity and connections several times. The only thing that doesn’t match exactly is the “Interior light panel with built in diode”...I had the prewired connector for the mirror in the headliner, used that and confirmed the connections to the CECM, but I haven’t found separate connectors to that component.

[ohecht]

Well, I figured out part/most of my problem. While I had 12v power to the mirror, it wasn't on the same circuit as in the diagram above, so that's what was causing the light sensor power error to come up most of the time (strange that the compass itself never had power issues, though...I think it was more in the diagnostic circuit than the actual power/ground circuit to the sensor). This happened because I'd installed a mirror with a compass before doing anything with the Auto headlights and just kept that source for the power since it was working and I didn't see a need for all the power to be on the same circuit (at the time).

I still might have to tweak how I have it powered as I think I'm putting power into the system in a place where it shouldn't be...I assume the CECM is where the power for this circuit should originate, but I'll try to confirm that with a multimeter as it's not clear on the diagram. The Auto lights work fine now...the only remaining minor issues are that the Auto setting on the light switch doesn't light up in Yellow as it did before when the sensor circuit wasn't working well (and I think that's how it should work), the parking light setting is not illuminated when the lights are on for some reason, and the compass stays on even with the key is out until the car completely shuts down that circuit either when I lock the car and arm the alarm or when it times out after several minutes parked...that's what makes me think I'm still bringing in power from the wrong place.

[ohecht]

I’m more confused now. It worked fine all day until this evening when the same light sensor error came back. The rear fog light warning too although not always together. Tried another headlight switch too and the same issue although the multicolor illumination on the switch is working on this one. I wonder if it’s related to the fog light issue as that light does sometimes flicker regardless of the three bulbs I’ve tried, and nothing seems loose at the bulb or socket...the flickering must be coming from earlier in the circuit.

[ohecht]

It’s working again...for now. But the sensor already threw an error when I shined a light on it to test it so it could actually be a bad sensor or just that the diagnostic part of the circuit is too sensitive.

I used the factory wiring diagrams to check everything again and switched my 12v power source to the black wire that was originally connected to terminal 1 on the light switch. That’s how the factory circuit gets power...that wire leads to terminal 58d at the instrument cluster. The wiring diagram above is no actual 12v power source in it...the OP must have had a car with auto-leveling headlights or other features that included another power source...wiring diagrams for cars with those features have a separate power source connected to Fuse 10 but my car has no fuse 10. I just reconnected the original wire that was connected to Terminal 1 of the light switch in addition to the new wire in the diagram above and it all works.

I still have the rear fog light error despite the bulb working fine...that’s a PITA I’ll look into next and hope this sensor works...maybe it will stabilize itself somehow with a factory power circuit!

[k909068]

It’s working again...for now. But the sensor already threw an error when I shined a light on it to test it so it could actually be a bad sensor or just that the diagnostic part of the circuit is too sensitive.

I used the factory wiring diagrams to check everything again and switched my 12v power source to the black wire that was originally connected to terminal 1 on the light switch. That’s how the factory circuit gets power...that wire leads to terminal 58d at the instrument cluster. The wiring diagram above is no actual 12v power source in it...the OP must have had a car with auto-leveling headlights or other features that included another power source...wiring diagrams for cars with those features have a separate power source connected to Fuse 10 but my car has no fuse 10. I just reconnected the original wire that was connected to Terminal 1 of the light switch in addition to the new wire in the diagram above and it all works.

I still have the rear fog light error despite the bulb working fine...that’s a PITA I’ll look into next and hope this sensor works...maybe it will stabilize itself somehow with a factory power circuit!

From the OP's pics, I bet he has factory xenon headlight, which featured with auto-leveling function. I know the PITA feeling when retrofitting go wrong like this, wish I could help you more.

[ohecht]

I guess it’s all part of the fun with projects like this. Definitely too much time on a feature I probably won’t use that much...I just want to get it to work consistently and understand why the error is at least somewhat intermittent. On my older cars it’s usually as simple as getting power and ground to the right places but the sophisticated electronic modules and diagnostics on this car make it hard to retrofit features like this unless you duplicate the entire factory set of options and configuration.

[mnataloni]

So I have the connector but when I plug it in I am unable to get the compass or dimmer to work. The plug seems to have power on one of the pins. Any ideas on why this could be the case?

[Gunnarrrrr]

Anyone here have this DIY saved or the wiring diagram that the OP made? Need the pics

[easyAudi]

https://web.archive.org/web/20180906...picture-heavy)
..includes up to reply #5..(via wayback machine archive from March 13, 2019)

[Gunnarrrrr]

https://web.archive.org/web/20180906...picture-heavy)
..includes up to reply #5..(via wayback machine archive from March 13, 2019)

idk why I checked archive.is but not archive.org - thank you

before you responded I spent some time with the wiring diagrams and this is what I came up with:

ch/lh - E102
1 T32a/17 J285
2 headlight pin 1
3 headlight motor(I may retrofit this later)
4 T32a/17 J285
5 ground
6
7 T32b/24 J519
8 T32a/17 J285

mirror - Y7
1 T32b/18 J519
2 ground
3 T32b/30 J519
4 front left door control unit tap into left A pillar orange connectorT17f/7 (for side mirror dimming)
5 front right door control unit tap into left A pillar orange connectorT17f/8 (for side mirror dimming)
6 Dome light pin 1

headlight - E1
10 ground (to tap)
1 switched power KL15
7 T32b/29
16 T32b/25 A3 Positive (+) connection (58), in dash panel wiring harness

[Gunnarrrrr]

Got it wired up and working, sort of.

auto headlights work, and coming home with the fogs works. but now I have a dipped headlight error. Going to code to HID's and see what happens, although I don't have level sensors so I'm assuming I'll still have the dipped headlight error. I have some OEM xenons I grabbed off of a 3.0/lighting package or whatever and never gave me an error until now. I'll also try the original halogens and see what happens.

Also, my mirror was already wired up from the factory, with the exception of the power source, which I had already wired when I installed the mirror awhile back, ran a wire from the T17f orange connector to a switched power source on the fuse panel if I recall correctly.

pin 6 on the mirror was already wired from the factory to pin 1 on the dome light connector so I skipped that step. Also, pin 3 on the mirror was already occupied, and so was the dome light's pin 11, but neither appeared to go to the CECM's corresponding pins 30 and 19, so I removed them and ran my own wires. I'll review the wiring diagrams and try to figure out where those (now dangling wrapped in tape) wires went.

I'm using the same ch/lh switch as OP which only has pins 4,5,7&8 present, which I guess should've been obvious since it doesn't have the range control knob. May try the switch with range control and get the rest of those wires in once I sort out this issue. Maybe last actually, since I think auto dimming side mirrors working should be the obvious next step. I have auto folding mirrors from an S4 on with auto dimming, I'll need to check to see if I can just simply tap into the orange connector or if I need to run wires to the door control module. pins 4&5 are also already occupied in my mirror so who knows, maybe its already in place.

Edit: pin 3 on the mirror for the non-auto-headlight cars goes to the reverse switch via the dash panel harness into the ECU box to the red connector behind the ECU, to the pin that the transmission reverse switch sensor(manual cars) or the reverse wire from the Tiptronic harness.

pin 11 on the dome connector is connected to pin 5 on the dome light connector (internally somewhere), which goes to pin 2 on the J393 Convenience system central control unit, on the T12h connector (12 pin, black) via pin 2 on the T17f orange connector.

[Gunnarrrrr]

Can't get the light sensor to work for the life of me. I reverted all my wiring to the OP's wiring and even ran my own pin 6->pin1 wire, and I still get 02104 - Light Detection Sensor (G399) 30-00 - Open or Short to Plus

Headlights are on regardless of the lighting conditions. Where is pin 3 on the mirror really supposed to go? This guide and the wiring diagram I have says pin 30 of t32b, although I found another guide where someone said pin 14. I may try that next.

Does anyone have the pinout for CECM 8E0907279F?

Also, I'm using mirror 4Z7857511 instead of OP's 8E0857511

[Gunnarrrrr]

Basically i’m an idiot, those mirrors I referenced don’t work (duh). they’re just compass mirrors. I grabbed the correct one today and everything is good. Going to go back and simplify the wiring a bit and contribute a little to this DIY. At least on the 04/05 cars that have a pre wired mirror harness, you can probably avoid running any new wires down the A pillar. Next up I’ll be getting my side mirrors functioning, and I’ll add that here too.


Sent from my iPhone using Audizine Forum

[m.callihan]

I know this thread is old, but I’m looking for some assistance on this. I retrofitted the auto dimming rear view and CH LH lights as described in this guide, and all is working well except my reverse lights no longer work. I have been trying to look at wiring diagrams but I’m having trouble figuring this out. I did attempt to remove the connector for the reverse switch on the transmission and jump the pins, but it still didn’t work, so I’m assuming it’s a wiring issue and not a fault with the reverse switch.
For reference, my car is a 2004 6 speed manual A4 and the wiring was already in the headliner for the rear view mirror, just not connected down in the driver side footwell.

[easyAudi]

w/photos, from archived capture 3/13/2019 .. covers thread comments thru 5/3/2017:
https://web.archive.org/web/20180906...picture-heavy)

edit: m.callihan - i don't mean this in response to your Q. Sadly, I'm not much help there, unless you haven't seen the wiring in post #2. I flipped to the start of this thread to learn, and realized photos did not exist. Hope it helps others getting started.