I did this a couple of years ago and documented the process with some pictures, but never had the time to write about it and ended up forgetting about it. Lately I've seen this issue resurface, so I decided I would tell how I disabled my electric steering wheel lock.
I bought my 159 used and it came with this error: "vehicle protection system not available". It relates to the electric steering wheel locking mechanism, I went to a nearby thief den
dealer and they charged me 35 euros for half an hour of diagnosis and the result was: "There is indeed an error, it's almost certainly a wiring problem, you need to leave your vehicle here, it will take a while". Looking at the service manual description, they imply the car will not work without that module, so a wiring issue shouldn't let me drive the car at all, so I decided to take matters in my own hands. First I ruled out the battery, I bought a new Yuasa battery but the problem never went away. Then I removed the connector and check the wires, they were all fine, even after I moved the loom around vigorously, that was further proff the wiring should be OK.
I contacted a less shady dealer and they quoted around 300 euros for a new steering lock unit, which is pretty reasonable but I didn't really want to pay that much for a feature I don't really care about, but the constant error message was really bothering me, so I decided to try and hack mine as it was broken anyway. This is the process:
First you need to take the trims that cover the underside of the steering wheel. To get the maximum clearance possible and make the job easier I also removed the driver's "leg airbag" (sorry, don't know the proper name), if you do this follow the service manual instructions. Messing with airbags is potentially dangerous, but I didn't really felt safe working with power tools in the steering wheel column with an airbag pointing straight at my nose. This is what you see after removing the airbag and the lower covers:
You are supposed to remove the shear bolts and then replace them with new ones but, as I already said, I don't really care about this feature, so I sed a Dremel with a cutting disc and I created a small groove on top of each screw, with this groove they became regular screws, so I took them off using a regular flat head screw driver. Look at the last picture in the end of the post to get a bigger view of the cut in the screws. This is the removed unit:
As you can notice, we have an additional security measure, there are 3 screws holding the cover in place and they have specially designed heads that make it easy to tighten but make the screw driver slip when you try to get them loose. I was going to drill them but they were made of some really though alloy, the work around was really simple: put the unit in a vise and get a flat-head screw driver with sharp corners, apply a lot of force on top of the screw driver for it not to slip and try to loosen the screw, eventually it will start turning and come out.
After you take the cover off this is what you see:
Now you just pull the PCB out and disconnect the motor wires from the board:
I'll link 2 higher resolution photos of the main board in case someone wants to look at resistor values or part numbers.
Even though I was getting the error on the dashboard, I could hear the lock operating and after taking the key out the steering wheel would actually lock and unlock after inserting they key again, so the motor was working properly. This led me to suspect these two switches on the vertical board with the blue connector:
These two switches, marked SW1 and SW2 act like end stops so the controller knows when the locking bolt reaches the fully open and fully closed positions. It would be tricky locating exact replacements and hacking different ones in place would also take a lot of effort, so I decided I would just get rid of the locking mechanism altogether and trick the controller with a small relay. Luckily, I had a handful of these:
These very useful little parts are called latching relays, they operate like any other relay, but you only need to apply a short pulse of current and they stay there, no need to keep supplying power, if you want to switch it the other way you can either operate the other coil or invert the polarity of the coil you applied the pulse on, this is the diagram of the relay:
My plan was to wire the old failing switches to the relay in a way where it is either closing the SW1 or closing the SW2. The coil of the relay is connected to the motor driver, this way when the controller wants to lock the steering wheel it applies power to the coil (thinking it is driving the motor) and the relay closes the SW1, the controller sees the Switch 1 closed and thinks it reached the desired position and stops supplying power. When the controller wants to unlock the steering, it drives the coil reversing the polarity (trying to reverse the motor) and the SW1 opens and the SW2 closes, the controller sees this and thinks the bolt reached the fully open position and stops supplying power to the relay. I don't remember if the motor worked at 5 or 12 volts, but the relay was rated at just 3 volts, so I added a resistor in series with the coil of the relay so it wouldn't fail prematurely.
This is the final circuit, I put a bit of epoxy in the relay pins to try and stop vibrations from breaking the relay pins, the black and red wires go the the old motor connector:
I tried this and all errors were gone (I think I didn't even had to clear the error using Multiecuscan, it was just gone). Considering the lack of errors a success, time to reassemble everything. I started by completely removing the old motor and lock from the enclosure. I probably didn't need to do this, it was probably nearly impossible but I was afraid that with the vibrations there was a small chance of that thing moving and eventually locking the steering while moving, I know it sounds silly, but I feel safer this way
Now I covered the hole with a thick piece of plastic cut to fit. Again, probably no need for this, but this way I know nothing comes in or out of this box:
This is the board with the relay already attached, I used two bits of foam so the relay wouldn't be flapping around inside, a piece of foam between the relay and the board:
And another piece of foam on top of that:
I put the PCB back in it's place and closed the lid. The old screws were a pain to remove, I replaced them with three 4mm stainless steel screws:
Finally I put the unit back in it's place and reconnected the wiring connector. I actually reused the old sheer screws, the Dremel cut worked so well than I can easily tighten or loosen them at will:
And, to this day (two years later), it never complained again