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Discussion Starter #1
Hi guys, I noticed today that the heating control unit in my car was dark when I was driving home, the backlight hadn't come on with the lights as usual. I turned the interior lights on to see what was happening and noticed that the outside temperature indicator on the heater control unit was also being faulty showing -- however the indicator on my clocks still showed 6 degrees c which is about right.
After I stopped and started the car again they seemed to start working again although there was a delay in the backlight coming on which is strange and definitely isn't usual.
Any ideas what the cause could be? All other functions seem to be working fine
Thanks in advance
 

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I assume you have Climatronic (automatic temperature control).

Just one possibility here...

I believe the outside temperature and backlight intensity are both transmitted over the Comfort Canbus, so there could be an issue with that bus. The Comfort Canbus goes to all the doors and is spliced under the left side floormat (I don't think there's any difference for right-hand drive).

Have you have water inside the car? Is some cases, the splices were terrible from day one, so they just have to be redone. As a test, can you lock/unlock all the doors from the driver's door while the malfunction is occurring? All the lock and window functions depend on the Comfort Canbus to get from door-to-door.
 

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Discussion Starter #3
You've nailed it in one. I'm currently investigating the cause of the drivers door working independently from the rest of the car, locks and windows included. I've already fixed the water leaks.
The splices under the floor look ok but I haven't yet done a continuity check on then, I read somewhere that there were two types of splices and mine was the better of the two (clear adhesive heatshrink coated). I think the fault is going to be inside the drivers door which is annoying as I've just applied silicone to the inner door card to resolve the leaks.
I'll update this thread once I've had a look. Thanks a lot for the help
 

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Discussion Starter #5
I have an aftermarket head unit in, I'm not sure how to run the diagnostics through the head unit regardless, could you expand on how I might do it please? Thanks
 

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2004 B5.5 Variant 1.8T
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I believe he means the diag through the climatronic head unit.
 

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Discussion Starter #9
Thank you very much.
538 - Canbus....
I've been at my canbus wiring today to try and resolve my drivers door controls, locks and windows etc. Found the splices near the CCM which were corroded so I reworked them both but still all the same faults present..... do I need to clear the codes with an OBD reader?
 

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Yes I believe you will need to clear the codes after fixing them as they are stored in the memory.
You will need to Use a Vag Com or something very similar to clear the codes. Generic scanners will not do this.
 

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You'll have to clear the codes in the Climatronic. The procedure is in the writeup. (Hold ECON for at least 2 seconds after the last code is displayed.)
 

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Discussion Starter #12
I did that and 538 (Canbus) and 4FA (recirculstion flap servo, although this works fine?) persist... I think ill have to start a new thread specifically on the CAN Bus as it seems there is still something somewhere which isn't playing ball.
 
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