I recently had to replace the alternator and did quite a bit of searching around for info on how. Most procedures say that you need to put the car into Service Mode. I found one post that said you could do it without Service Mode. Unfortunately, it's skimpy on details, so I decided to write up the full process I went through. As always, undertake this job at your own risk, your mileage may vary, and the amount of blood shed may be more (I didn't lose much) and left/right always refers to the drivers viewpoint.

1. Remove the battery cables.
2. Dismount the coolant reservoir so you can move it out of the way (like during an oil change).
3. Across the top of the grill there are 4 button clips. Remove them.
4. On each headlight there are 4 bolts holding the unit in place. Remove all of them. Note that on the right headlight, the bolt holding the unit to the upper frame uses a threaded washer thing on the underside so it's easy to lose if you don't know about it. Also note that of the 4 bolts, 1 is shorter. It's the one to the upper frame.
5. On the left side of the upper frame there's a black plastic block looking thing, about the size of a USB thumb drive, twice as long. Under this is a connection in the hood release cabling. It pops off/up and you can disconnect the two.
6. While you're at the cable, right there is another button clip holding the window wash tank. Remove it.
7. Following along the upper frame, there are a number of bolts to remove. Two at the strut column. One about 2/3rds of the way down. Two torx for each of two bonnet latches. Once all are out, you should be able to pull it up and lay it across the top left side of the engine, opening some room over the alternator.
8. Remove the dipstick tube. You'll need to pop off the two wire bundles tied off there. There's one bolt holding the tube. Once out, take some masking tape and cover the dip stick hole so nothing finds its way in.
9. The wire bundles in step 8 are for the upper O2 sensor. They connect together at a bracket to right of the heat shield. I recommend you pop the entire connector out of the bracket, using a flat screwdriver to push it toward the front of the car. Then you can handle it and separate the two so you can remove the O2 sensor without twisting the cable.
10. Next remove the connector bracket.
11. Time to remove the heat shield. I pulled it and in hindsight, I wonder if it was really necessary. If there is a next time, I'm going to skip removing the heat shield and the O2 sensor and see if it really is necessary. In any case, there are 3 bolts along the base of the valve cover. Three more lower down facing the radiator.
12. Remove the hard plastic intercooler to intake tube by disconnecting the airflow sensor wire and the clamp up by the right strut column. On the lower end of the tube you have two options. There is a rubber L hose that connects it to the intercooler. I disconnected the upper end but the bottom would work as well. If you leave the rubber hose on, it's in the way a little bit, but you can push it out of the way easily.

At this point the removal and replacement are the same whether you put the car into service mode or not. The hardest part of this method is the removal of the bottom 3 heat shield bolts (#11). Service mode would have made this easier, but I'm not sure it would have been faster overall. Another thing to know is that you can jack up the car (use a jackstand for safety) and remove the right wheel. Pop off some of the plastic clips and you can fold the cover back, revealing another way of getting at the bottom alternator bolt.

The alternator is held on with three E10 Torx bolts. These are the external version, the mirror view of most Torx. Accessing the bottom one is a bit tricky because there's a metal AC tube in front of and almost in line with it. If you strip it, it's a $10 bolt. Also there's some bushings on the alternator bolts, some on the block, some outside. Make sure you locate and keep them.

These cars are fitted with either a 120A or 150A alternator. On the back of the alternator, my 120A had a manufacturer name of Valeo. Even the dealer couldn't tell me from the VIN which one, he said they pull it to find out. Check realoem for pictures of the two. Using the pics you you'll see the housings are different and should be able to tell before pulling it. The Valeo mark was a confirmation I had the right amp.

The short summary for the removal is 1) use a large wrench to back the belt tensioner off, lock in place with the spring loaded pin in the bracket, 2) remove the the alternator cable (bolt) and a wire (plug), 3) remove the upper two alternator bolts and the tensioner will come out, 4) remove the bottom bolt. Pull it out.

 

Sweet write up. This will most definitely help.

Be careful with the Torx Bolt in front of the AC Tube. If you apply too much pressure on the tube you can stress it and cause it to leak.

While you can reach the Alternator without putting the R56, R57, R60 and R61 into service mode. It makes it much more easier.

With patience and the following instructions posted above by mysticturner and you will be on you way to life with a new Alternator

 

While it would be easier, service mode won't help with space regarding the AC tube. That part doesn't move out with service mode. So Manny is right - BE CAREFUL when working on that bolt.

I don't know if such a tool exists, but I would have liked to have an E10 ratcheting wrench (like the wrenches you see with an open end on one end, closed on the other and the closed end is actually a rachet). I would have used that through the wheel well. I ended up putting the new bolt in (how'd you think I know how much it costs?) with an E10 socket 3/8" drive, to a 3/8" to 1/4" adapter, 1/4" to hex adapter, and a 1/4" closed end socket on the end. Just narrowed enough to not push on the AC pipe.


Grinding off the head with a dremmel tool works too.

 

8mm will work on an e10 torx. so you can use an 8mm wrench if you dont have a e10 wrench.

 

Thought I'd pass on this suggestion as it saved me a lot of time and blood on my 2010 R56 Justa when I replaced alternator this weekend......I followed the process above, got the alternator unbolted but just couldn't get the alternator out of the engine bay - just too tight of a fit to squeeze it though the space between the engine, manifold and the radiator. No matter how I twisted, turned or pulled it wasn't fitting through this space. I was going to put the car into service mode but really didn't want to go through all the trouble of doing this. After thinking about it I remembered what I had to do to change the water pump which was removing the engine mounts and jacking the engine up. I put a jack under the engine to support it and remove the right side upper engine mount. Once I did this I was able to push the engine to the rear of the engine compartment which gave we about 2 or 3 additional inches to work in and removing the alternator from the engine bay was a breeze. It also made installing the new alternator and bolting it in really easy.

 

thanks for posting this, Not there yet but will be doing this soon and I want to keep this info handy when I do.

 

I followed this guide and it was great. Service position takes me ages! Small tip, to know which alternator you have, shine a torch down there and if it has a black central band then it is 150amp, if the whole body is silver it is 120amp (also depicted on realoem.com) even the Chinese copies look like this.

 

Just did this on a 2012 S hatchback. Followed instructions in this thread and all helpful hints by others. No need to remove the catalyst heat shield. In order to get the bottom bolt out on the alternator, the one blocked by the AC line, we removed the 2 easy bolts and loosened the 3rd bolt, blocked by AC lines, on the AC compressor to allow enough wiggle room to get the bolt past. On reassembly, it seemed like tilting the AC compressor clockwise pivoting on the 3rd bolt allowed the alternator bolt to squeeze by. The local part stores seemed to stock the 150 amp (black stripe) alternator so hopefully that is the one you have. It was also cheaper than the 120 amp unit. We ended up taking off the front bumper cover, intercooler (to get the hard pipe completely out of the vehicle), and removed the passenger side engine mount to raise the engine with a jack on the transmission 2-3 inches to get the alternator out the top. We removed the bracket that holds the AC fitting near the dipstick (torx bolt) and that gave more space to wiggle it out.