Thanks CL770. The tune is not new. It will have been done over 10 years ago. But I take your point that the tune probably isn't responsible for the engine light. That will mean the mechanic will need to start from the last error code in the file (#NO steering angle message) and gradually eliminate each.

According to the diagnostic report from the mechanic, the vehicle software version is V10.48. Is that the ECU version?

I'm wondering about taking it into a tune shop for them to assess it for me. It would pay to understand, and have a record, exactly what has been modified. What do you think?