A4 Cabrio boot lock and roof electrical fault

[pompeyal]

Hi all, My car is a 2006 A4 Cabrio and I have an electrical fault and would like some assistance if possible, I have trolled the forums covering similar faults and I have done some investigations, what happened is the battery went flat for no apparent reason and when I started it again the following faults appeared:-

1, the boot would not open using the remote control (the doors work fine)
2, the roof will not actuate (Open or Close)
3, the battery drains after approx. 24hrs. (If I drive the car daily the battery holds till the next day)

What I have done so far:-
1, I have checked and fully charged the battery, that is fine 
2, I have checked the switches at the barrel, latch, and release mechanism, they function correctly
3, I have checked the actuator that is fine
4, I have manually opened the roof and closed it to reset and nothing different, (roof does not work and i get not available message, on switching the ignition on the roof warning icon on the dash flashes until I start the engine)
5, I have checked the loom from each switch and the actuator as far as I can back to behind the right hand boot lining for breaks, none found.
6, I have metered the earth (brown cable) at the Actuator, Barrel, Release and Latch they show good grounding.
7, I have metered the Barrel live (Blue cable) that shows no voltage
8, I have metered the Latch live (White cable) that shows no voltage
9, I have metered the release live (Grey cable) that shows 12volts
10, I have metered the Actuator live ( Red/Yellow cable) that shows short to earth.

Can anyone please help me further? I believe the roof doesn't work because of the boot release has a fault and it the roof electrics can't determine if the boot is not shut it will not open.

Questions:-
Is there a relay that may have gone faulty, if so which one and where do I find it?

Has anyone got a wiring diagram which covers the boot harness and where it is controlled from?

I have seen several times people who have had the same symptoms and the majority of the time there has been broken wires or the boot release actuatorhas gone faulty, If only that was the problem with mine but its not, has any of you guys had the same problems as me, if so how did you overcome them?

Cheers Alan

[pompeyal]

Right after spending more hours on this problem to no avail has anyone got a wiring diagram for the boot latch activator showing the red/yellow wire route and termination please?

 

Alan

[Magnet]

Hello Alan,

Sirty to hear of your troubles.

A couple of questions:- when you say you have charged and checked the battery and found it to be OK, does that mean you have charged the battery and had it tested and evaluated its % efficiency? If yes, then obviously you can discount the battery. If you haven't actually had its efficiency checked then you will need to. 

You say the battery will discharge (if left connected on the car?) in 24 hours. Assuming you have had the battery checked snd it is serviceable then something is still "running" when the car is switched off, and that current draw will be in excess of 2amps, and that would equate to some part of the curcuit demanding over 24 watts of power - high! - to say the least.

If this is truely the case ( and personally I would disconnect the battery for 24 hours and confirm it then holds it charge) the you will need to establish which curcuit is at fault. You won't do this with your average multi meter since they generally will only accommodate mA of DC current. If you have a meter which will hands say 5 amps DC then you will need to take the earth lead off  and connect the meter between the battery earth terminal and the earth lead and measure the current. You then remove each fuse in turn until the current draw reduces to next to nothing. Obviously the removed fuse points you towards the curcuit which is at fault. 

Such faults can sometimes be associated with broken wires where the cabling goes into the boot via. the flexible sheathing.

Kind regards,

Gareth.

p.s. Courtesy lights would need to be isolated if you have the door open. 

[pompeyal]

Thanks for getting back Magnet, as you have read in my posts, I am pretty sure the red/yellow cable from the boot latch actuator should not read short circuit but when switched it would show voltage, as this cable shows a short circuit to earth would this not be the problem area? I will go through the procedure with the meter across the earth terminal and lead and pull fuses to try and find the circuit, I can't find any info on the boot release fusing anywhere on the master fuse box, I have pulled the front door fuse whilst monitoring the short on the red/yellow cable  at the actuator and it still shows short with the fuse removed, I removed the comfort control unit fuses and it still showed a short, does the boot share another fuse with something else do you know?

 

[radish]

Hi Alan, i know this is an old thread but did you solve this issue? My red/yellow shorts to earth too and am struggling! 

 

Cheers 

[pompeyal]

Hi Radish, yes after a wild goose chase I finally found out the cause to my problem, there was a short circuit on the glovebox locking motor which was blowing the fuse to the comfort unit under the carpet in the passenger footwell, one of the plugs that is on the unit has only 2 wires which supplies the motor, I have removed the plug from the comfort unit and now the fuse stays as it should, both of the wires of this particular plug are both shorting to earth. I have used my Foxwell Pro scanner to finally sort out the problem, several times when checking the errors most of the faults were leading to security problems such as errors on door locks, petrol filler cover locks which were thrown up when locking the car using the fob, each time the comfort unit fuse blew. since removing the plug all as been well. The roof electrics is controlled through the comfort unit and when the fuse blows you get the roof error message (roof unavailable) try replacing the blown fuse and try the roof, I did and it worked as normal until I locked the car and the fuse then blew. I hope this helps you sort out your problem because I know how much frustration you must be going through trying to find this fault, it took me ages to finally find exactly what my problem was. The glove box lock motor is only activated when locking the car as it locks the glove box then. The boot problem also went away after removing this plug, I am sure this problem was caused because they share the same circuitry.

[radish]

Thanks for this info I'll try and look today. I did test all the fuses last night and all ok, there is only 1 fuse box? Side of the dash?

 

I think I may have a problem with comfort unit, I have 12 codes that wont clear!

01330

01331

01332

01333

01334

01368

01369

01370

01371

00532

Most of them relate to alarm being triggered. 

 

Cheers 

[radish]

It looks like I'll be booking it in with an auto electrician. 

I pull the 2 wired plug tonight but no difference, all fuses are intact too. Must be a break in the cable.

 

Cheers for the help 

[pompeyal]

Sorry I couldn't help...

 

[Petrol head]

On 6/4/2019 at 3:28 AM, pompeyal said:

Hi Radish, yes after a wild goose chase I finally found out the cause to my problem, there was a short circuit on the glovebox locking motor which was blowing the fuse to the comfort unit under the carpet in the passenger footwell, one of the plugs that is on the unit has only 2 wires which supplies the motor, I have removed the plug from the comfort unit and now the fuse stays as it should, both of the wires of this particular plug are both shorting to earth. I have used my Foxwell Pro scanner to finally sort out the problem, several times when checking the errors most of the faults were leading to security problems such as errors on door locks, petrol filler cover locks which were thrown up when locking the car using the fob, each time the comfort unit fuse blew. since removing the plug all as been well. The roof electrics is controlled through the comfort unit and when the fuse blows you get the roof error message (roof unavailable) try replacing the blown fuse and try the roof, I did and it worked as normal until I locked the car and the fuse then blew. I hope this helps you sort out your problem because I know how much frustration you must be going through trying to find this fault, it took me ages to finally find exactly what my problem was. The glove box lock motor is only activated when locking the car as it locks the glove box then. The boot problem also went away after removing this plug, I am sure this problem was caused because they share the same circuitry.

Hello Alan,

Does this vehicle has Glove box locking motor ?

Is there any separate switch for closing the glove box ?

Sorry if it's a stupid question,just wanted to know about the function.

Thanks for your consideration,

Jose