Audi A4 Boot lock touch pad / unlock button fix
It seems to be a relativly common fault, and thought i would throw up this how to guide as i had a look at mine today.
1. remove the boot lid liner, loads of screws around the edge, two in the handle, and a few around the warning triangle holder.
2. un plug the two yellow connector onto the back of one of the pads/ buttons and see if there is power. mine clocked up 10.5 volts. if there is, your in business. try short circuiting the two wires with a bit of wire to basically bypass the switch, and the lock should release. you can slide the top off the yellow plastic connectors sideways to gain easier access to the wires.
if the lock releases then its the switches at fault
3. un plug the number plate lights and remaining touch pad.
4. undo the 4 bolts holding the rear 'plinth', two on either end, and two holding the lock barrel, you can then pull the barrel out the back (i just left the barrel hanging, seemed happy enough, careful not to damage the linkage)
5. push the clips together on the back of the no. plate lights and the plinth thing should come off.
6. unclip and slide the touch pads out of the plinth.
7. remove the rubber cover from the touch pad, this should just pull off, might have to slip a screw driver in the edge. you should be greeted by somthing like:
that large corroded metal plate pivots in the plastic switch, pushing on a mirco switch. these obviously corrode jamming them selves in their own corroded powerded.
8. carefully slip somthing down the side of the metal peice and pop it out, taking care not to damage the plastic.
9. clear out the white crap, i used some wire wool / scotchbiright and some sand paper. it will never look great but you just need to shift the worst of the corrosion and get it all clean.
there is a small lump on the metal peice that just touches the mirco switch, be careful not to sand this off!
10. clean out inside the plastic switch area, the tiny micro switch has a little black nobble on it, at some point one of mine had been forced and this has been broken off. probably by me in my frustration that it didnt work!
if you dont have this, you will have to build up the lump on the metal bit. i havent tried this but will do soon to try and get my other one working.
note little black bobble is present in the middle of the red bit, take care not to break this off.
11. put the metal peice back in, i smeered mine with lithium grease first to try to stop it getting any worse. the metal bit should pivot and there should be a little 'click' from the micro switch.
12. poke the wire through the hole in the boot lid, plug your finished button in, and test it.
13. repeat on the other one and re-install.
hopefully that should fix it! i dont know how much VAG charge for a new one, but i expect its quite a bit saved!
tomo i will try building up something on the metal plate to replace the broken micro switch bobble, will let you know how well this works.
at last, i can now open my boot without turning the engine off!