My HUD had slowly gotten progressively dimmer, which I initially paid no attention to, then one day it just quick working, ie, no display. I could see the mirror moving up and down with the controls (so it's not from a fallen mirror), but no light from the display or inside the unit viewed in the dark of night, from all different angles. And no, the dimmer switch was not turned all the way down.
I have seen posts by others here of dimming displays and saw a repair on video of bypassing the light sensor (photoresistor) in the HUD unit to correct a failure of that and restore the display. It bypasses the function of the resistor (to change the light intensity from day to night) and lets you control the brightness of the display with the control for the HUD alone.
So today it bit the bullet and took the dash off and removed the HUD unit. The wiring harness was a little stuck in the IPC (dash console) but came out OK with a little back and forth wiggling and gentle pulling. I seriously doubt if I pulled any wires out of the harness plug. it came out clean and everything seems solidly connected inside the plug.
I took the HUD apart and soldered the connections on the back of the little board for the photoresistor (on the diagonally opposite corner from the photoresistor) together, like shown in the repair video. I touched nothing else. I closed it up and then reconnected it to my dash and now I get nothing, no display, no mirror movement, no response to any of the HUD controls. Before I took it all apart at least I had appropriate mirror movement. I also checked the harnesses going to the IPC and to the HUD controls and they are solidly connected and I never touched them either,
I tried the trick of disconnecting the battery for 10 min to see if the computers would reset, but that did nothing but give me 2 more problems.
When I turn on the car now the DIC tells me to Service Active Handling and Service Traction Control. I was thinking that because my interior is all apart and the Active Handling button on the console is not connected, that might be a reason for the new messages and codes. Could that be true? I never had these messages before.
So where is the fault in my HUD? In the HUD, the IPC, somewhere else? And will those codes and messages go away when everything is back together?
The last little problem I have is that I cannot get the wiring connection to the glove box light apart, I must be missing something, so somebody please tell me how to get it apart. Right now I have a trickle charger attached to the car so I don't get a dead battery if that light doesn't time out.
Thanks.
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Use the On Board Diagnostics to see what codes you still have. There may have been codes that indicated a specific issue with the HUD before you disconnected the battery. Did you accidentally over heat the circuit board when soldering on it?

Bill

 

There were no codes before today, no co0des before I disconnected the battery.
There basically is no circuit board. only a direct path from the sensor to the connected wire on the opposite side. There are no electronic components to that item.
Here's a pic of the back of the board where I soldered the 2 contacts together, seen at the lower right corner.

 

Did you verify you are getting power through the cable to the HUD? If not, maybe be a fuse issue.

 

The HUD ribbon power and info cable plug into the back of the IPC, How do you verify power going to it?

 

 

So today just for the heckofit I looked at fuses 19 and 25 to the IPC and they were both good as expected (the IPC works fine and all lights for the gauges and HUD controls also illuminate when the lights are turned on).
Since the HUD control panel illuminates when the lights are turned on and respond to the main dimmer switch, I know this little panel is getting power to it.
When I work the mirror height adjustment buttons on the HUD control, the mirror can be seen to move up and down, but there is still no display, no illumination inside the HUD unit, no response from moving the dimmer switch up and down multiple times. So I also know that power is getting to the HUD display through the control panel.
So either my HUD unit is caput, the display is dead (how many rare times does this happen?), or the dimmer slider for the display is shot.
Any way to test either part further or do I have to buy another HUD unit and hope for the best?

I also have no codes today on the DIC, so at least that that's a plus.