Cabrio problem

[pompeyal]

Hi all, bet none of you can help but here goes, I have a 2006 A4 Cabrio which has the following problems, they all happened at once so....1, the boot will only operate using the key, the switch and the fob do not work, I have checked all the wiring from boot to the comfort unit under the passenger seat and all OK, no breaks or shorts, the actuator is functioning as well as all the boot operation micro switches. Have looked inside the comfort unit but nothing obvious and circuitry checks out. 2, The roof does not operate under power, only manually, dash says not available when trying to operate by the switch, I have manually opened and shut the roof several times as some suggest as a fix to no avail. 3, The battery keeps draining.

What I have noted is that the power cable to the boot actuator reads short circuit but I do not know if that is the default when not in operation, I have checked the cable run for breaks back to the comfort unit and checked continuity end to end and for shorts with the cable disconnected at each end and this proves OK.

I am thinking maybe a relay has broken down the other side of the comfort unit causing the short which is draining the battery, all fuses in the main fuse box are OK.

Any suggestions please..

 

[Magnet]

Hello Alan,

Without being patronising, it would seem to know your way around a volt/continuity meter, so I guess you should be off to a good start. 

If we start with your last mentioned issue - the battery is draining. To me this would be my first port of call, and I would want to find out why, before I worry too much about the roof not working. Maybe part of the same problem, but maybe it is, until it is proved to be. 

To do this you will need a more sophisticated meter than your average DC/AC volts and resistance meter, since you will be measuring currents and likely to be subjecting the meter to greater currents than the mA most meters will handle. Blown meter will be the result otherwise!

 The logic is simple - you connect a lowish current amp meter between the removed negative lead and the batery post (switch off your interior lights etc. ) and measure the current taken after the alarm has 'gone to sleep'. This should be mA, but if the battety is draining then it will be higher. Now remove each fuse in turn until you lose the current drain. That will be the fused curcuit which is at fault, and you will now need to find the fault in that curcuit. It could quite possibly be the roof curcuit, but you need to confirm or refute that before assuming.

Back to the roof issue:- I would have a guess ( and a guess it would be) that your 'shorting' problem is in the section of harness that gets flexed when the boot is opened and closed. I appreciate you have tested it but such areas are notorious for cracking insulation as the harness continually flexes over the years. Obviuosly this time if year is worse as the harness hardens in the cold weather.

Good luck with your checking, but very often such annoying faults are worth an investment of a couple of hours with a local trusted auto electrician.

Kind regards,

Gareth.

 

 

[pompeyal]

Hi Gareth, thanks for the reply I will get onto the checks as soon as I get hold of a suitable meter from work, as far as the cable breaks go, I have stripped back all the bindings on the boot harness as far back as the boot bulkhead going into the cabin and no damage there, that was my first port of call, thanks for the mention though.

 

Regards Alan