So, I played with the S4 a bit last night... by changing the wiper motor and mechanism out for a quiet one (God, was the old one noisy!) and adding some aero wiper arms and blades from a late model B5.5 Passat.
In the process of replacing the wiper mechanism, I had to take the lid off the ECU box and unbolt it to move it out the way so that I could get the mechanism out.
I went to the car this morning and the battery light was on. When I rev the car, the volts on the dash go up from 12 to 14/15 and then stay there. The mileage counter doesn't seem to be adding the miles on either. Also, my 'miles left' figures aren't working either. Sometimes it reads 00, then it'll read 75... even thought there's still 3/4 of a tank of fuel in there.
I'm thinking I might have disturbed something within the ECU box.