Steering Angle Sensor Alignment
It's quite common for steering wheels on 700cc smarts to fail the alignment coding
The steering angle sensor found in the black cartridge on the back of the steering wheel for
700cc fortwos and Roadsters have a knack for going wrong. What normally happens is the
steering wheel is removed and whilst it is off the cartridge is accidentally moved.
Moving it a bit left and right is usually fine, the problem starts when it makes a full rotation.
The cartridge looks straight but electronically it isn't. According to the car it will be out of
alignment by far too much to pass the coding phase of wheel alignment.
To align the steering wheel with the MB Star or Win Star hardware, the wheel is positioned
straight and the alignment program is run. Upon starting the program the wheel is turned
left, then right then back to centre. If the resting position is 0 degrees, the left and right
movement is usually anywhere between 90 and 120 degrees from centre.
Upon doing this the program should pop up a screen declaring the success
of the alignment but quite often on 2nd hand steering wheels you get a screen
appear stating that the alignment was a failure.
So, What To Do?
Most companies immediately mark them down as dead but all is not lost yet.
With the steering wheel off, look at the back of the ESP cartridge, remove the 4x Torx10 screws.
The cartridge shown below has been removed from the steering wheel but this isn't necessary.
With the screws out, the cover lifts off easily. Look at the unshrouded connection circled
blue below.Take a paper clip and touch all 4 pins at the same time to short them out.
This grounds the circuit and ensures that you are starting with a clean slate.
The first thing you need to check is the orientation of the full rotation sensor, this
is the cogged wheel circled at the top of the next picture. This cogged wheel has a
magnet in 1 sector, make sure this is in the position shown below (hidden under the copper
coloured ring). If not, turn the copper ring 1 full rotation anticlockwise to magnet go clockwise
and vice versa. Make sure the magnet travels the shortest distance to the position shown.
Below the full rotation sensor is the optical rotation sensors. These read the upper and lower
holes in the copper ring. The inner holes are the pulse code which tells the car the speed the
wheel is being turned. The outer holes indicate which direction the wheel is being turned.
When the steering wheel sits on the car at 0 degrees, the copper ring sits in
1 particular position.Take a look again at the full rotation sensor, line the
central point up with the larger of the 2 holes on the inside of the disc.
With the large hole in position you should see a plastic nub situated in front of the optical sensors.
Here is the disc aligned with the 2 points shown above.
If you spin the cartridge over you should see the manufacturing date stamp facing straight up.
This gives you a good idea how much the cartridge has moved and in what direction so when you reassemble it you can very quickly shift it back to the correct resting place. A line of sticky tape across the face of the cartridge will stop it moving until you refit the steering wheel.
Thanks to Alain for pointing out my error. All fixed now.
This info was added 02/12/2010. I find it sad that I have to put dates on here but all too often
I find my exclusive info appear on other sites with them claiming full credit for my work.