It took me just over 1 hour to complete and is a nuisance of a job due to tight access and poor visibility. You will need the following -
Torch
Screwdriver (philipshead)
Torx T20 (I used a small ratchet) magnetic head if you can
Small mirror to get my bearings
You will have to remove the panel below the steering column to gain access. 3 screws at the front, 1 behind the clutch, 2 clips just below the steering column and a clip in the corner at the centre console.
Drop the panel down slightly and remove the 2 connections for the footwell light and the OBD2 socket.
Slightly behind and to the left remove the 2 connections from the round green bit (I know I'm very technical
) and carefully remove the panel
Looking at the back left of the footwell remove the foam padding ( pulls straight out ). You will now be lying in the footwell with the side of your head hitting the brake pedal to get the view in the pic below. Behind the heater duct you can just see the edge of a white plastic disc above it and half a dozen wires directly below it, the hedgehog is behind this. I went and got a cushion at this stage because my side hurt lying on the door sill.
At this stage it is advisable to chase away small children and those of a delicate disposition as even the most mild mannered person will turn the air blue from here on in !
In the pic below I have already removed the bottom screw (torx T20), don't worry about disconecting the 3 wires into this unit as you can work round it. The 5 wire connector is plugged straight into the back of the hedgehog but it's easier to get out once the bit in front has been removed. You can just see at the top of this pic a little clip holding it on and this will slide out once you get the top screw out ( torx T20 ). This top screw is so well hidden I couldn't even get a pic of where it is. Look at the white plastic disc ( you can just see the side of it in the previous pic ) and put a finger to the left of it along the top of the unit, pushing your finger back you can just feel the edge of a curved recess were this top screw is hiding. The unit will slide neatly out once this screw has been removed and you can then remove the connector at the back of the hedgehog.
Remove any screws holding the hedgehog in ( none in my case ) and there is only a clip on the right hand side of the hedgehog holding it in ( see pic below, to the right of the brown wire). I pushed the clip in with a large screwdriver in my left hand and jiggled the hedgehog out pulling on the connection with my other hand. Once you pull it out a bit you will need to push up on the metal rod shown in the pic below to allow you to remove the hedgehog completely.
The hidden screw captured for posterity, well actually to show that you will need a tool no fatter than mine to fit down the top recess to remove it. Admittedly this did take me a while to realise and scavenge a slim enough bit and was the cause of some very colourfull language.
Just to show the difference between old and new
Clip the new unit into place, pushing up on the metal rod again and jiggling furiously while swearing at it. New hedgehog clipped in shown below, reconnect the wires and screw in the unit again. I went for a short drive after this stage to check the heating was working as it should before coming home to put the rest of the dash back together.
I must admit that I failed to replace the hidden screw at the top, I gave up after a couple of attempts as the unit seems to be held in place tightly enough without it.
Hopefully this will be of some use to anyone else attempting the same repair although it should be stressed that I am no expert and there may well be a better method of replacement.
Cheers, Stu
it s a bloody nightmare ............well done you for posting this 
but atleast its changed now and I even managed to get the second torx screw back in too . I must have had the early symptoms as the only fault with my old one was the fan speed surging. Result though and thanks again for this thread should deffo be made a sticky as its a common problem in the E46 !
feel free to post them !
