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Discussion Starter #1
Hi All,
I have a problem with my Audi Q3. In my car are the tail lights always off and the lights in the bumper always on. I have seen a lot of topics about it and mostly is the Hall sensor in a wrong place or the micro-switches in the lock in the tailgate are damaged. I have checked both. The Hall sensor has on one wire a 12VDC PWM signal (period 20ms, duty cycle 40%). I suppose this is the PWM generated by the Control Unit - it doesn't change with the sensors position. On the second cable is a similar PWM signal (period 20ms, duty cycle 40%) but with max voltage 2.5VDC when the tailgate is open. When the tailgate is closed, the PWM gets down to about 0.5VDC.
I have checked also the lock. When the tailgates lock is open, pins from micro-switches are shorted together (grounded). When the tailgates lock is closed, both micro-switches are not shorted. I have checked it in an other car and it seems it's a proper behavior.
I have also the timing between those sensors - the Hall sensor and both micro-switches because I saw also that this is also important. I have assembled all together, checked the signal from the Hall sensor and powered off the car (I have also disconnected the Control unit). After connecting all back together the car should see the signal from the tailgates lock and the Hall sensor in the same time but it didn't help.
Is there an option that it's somewhere saved in the Control Unit that the bumper lights should be always on and the tailgate lights always off? Am I able to change this using VCDS? I have also replaced the Control Unit with an other one but without any success.
What is also interesting, when I press the brake pedal, the stop light on the tailgate lights up a little. I have measured this also and the light goes on every time for about 20ms (with correct voltage - 12VDC).
I have no idea what else I can check and what else can be damaged.
Please help :).
 

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This sounds very weird - like a transient ground fault or short for example - and NOT a normal VCDS selection. I am sorry to say that I believe you need some serious electrical diagnostics - best handled by your dealer imho...
 

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Discussion Starter #3
Hi Roger,
thank you for your reply. You're right - it was a lead problem but I have finally found out why the back light on the tail gate is not working and fixed this. Tail lights are working now like they should - they're on when the tail gate is closed and off when the tail gate is open. Unfortunately I'm still fighting with the bumper lights - I can't find out where is the magnet that is activating the Hall sensor to turn off the bumper lights when the tail gate is closing. When I'm manually moving a magnet near the sensor then it works good but without this magnet it's not working.
Best regards.
 

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...wish I knew exactly where it is to point you - but alas I don't. Will try to inquire of experts above me though ...
 

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Hi I have the same issue on my Q3 can you tell me where you had a damaged lead/wire so I can have a look to see if its the same.
 

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It can always be the turn signal switch itself Audi Q3, but I'd test first with a good volt-ohm meter the circuits passing through the T5 connector right next to the switch on the wiring diagram (Bentley 4--appendix D), and test the headlight switch and emergency flasher circuit since these circuits are all interrelated. This is usually a miswiring such that the light gets power direct instead of through the flasher.
 

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Hi Guys
I am having the same problem with my boot lid lights. When I indicate or brake, the lights in the bumper work but not on the lid. This is with the lid closed. I've checked the connectors in the latch on the body and also in the lid. All appear good. Ive tried wd40 just to drive out any moisture. My boot lid appears misaligned and sometimes it catches and locks and other times it has to be 'helped' to lock. One of the hinges, you can see about 8mm of the undercoat paint as if it has dropped slightly. I tried using the adjustors on the lid but they do little. So i think my problem is related to the boot not sitting right and failing to then energise/de-energise the microswitches. Incidentally, the switch on the actual catch is always acting as a magnet whether the boot is open or not, is this right - i think this is the hall switch? It seems these issues are pretty widespread so I thought there might be more online but sadly not. I tried disconnecting my battery to reset it and this does work until i open the boot again when the fault returns. All wiring is in good shape so it is either the boot not sitting right or one of the switches....is there a way to reset the timing referred to between the two switches altering state and anyone know what the logic is for this. Can I just short both switches or something to get the lights on the boot to function? With the hall switch is it sensing the little metal stripe on the flap moving away from it as the latch enters the housing or the fact the latch has entered and the metal on the latch itself?. I'm wondering if some foil or other might temporarily fix it?

Lots of questions i know. And just to help anyone...when i disconnected the battery to reset it, i got a power steering light on the dash. To cancel it, centre your wheel. Then hard lock left. Wait 2 secs. Then hard lock right. Wait 2 secs. Then centre. It should then go out. If not switch the engine off and then on again and it should go out.
Here's hoping i can get it fixed!
 

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Guys I have fixed my rear light issue. To recap...I had the lights on in the bumper but not working in the boot lid. The fault I had relates to the Hall sensor fitted adjacent to the lock mechanism on the car body. It is next to the silver flap that is pushed open when the lid closes by the lock going into the recess and catching.

What I found when I took the cover off to expose the hall switch is this...

The hall switch should be energised and if you put a screwdriver to it it should attract the screwdriver as it is magnetic. The little silver flap is retained by the plastic housing and is on a hinge. The hinge is springloaded to hold the flap closed. On the side of the flap is a little lug and when closed this is adjacent to the sensor. The hinge is held still, to prevent lateral movement, by two small plastic lugs. On mine the plastic lugs had bent allowing the hinge and flap to move, literally only 5mm or so. This meant the hall sensor wasn't ever registering the flap and so sending the wrong signal to the computer and switching the bumper lights on and the boot lid lights off.

I moved it back towards the sensor and the lights then started to work as they should.

On the boot there are four adjustors to control how far the boot closes. They are on the inside of the lid and can be adjusted by screwing them in and out. These were wound down too tight allowing the boot to be pulled closed too far and thereby bending the little lugs.

By me adjusting those and straightening the little lugs up, the hinge and flap are closer to the hall sensor but i think i am going to have to fashion a more robust solution to stop the hinge moving back again.

Hope this helps anyone with this intermittent issue. I'm gojng to fashion a plastic lug and araldite it into place to keep the hinge and flap still and prevent it slipping away from the hall sensor.
 
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