I read many topics on this forum in the past, and they helped me to solve quite a few issues – thank you all BMW guys! Now I decided to share my own experience in solving what seemed to be a serious issue, hoping that someone will find this useful.

I have 2009 E60 520d with 170k miles on the clock (which is not bad for 6.5 years old). Few days ago, a warning message came up while driving on a motorway:

Drive control system – Drive moderately

Immediately followed by another warning message:

Start assistance inactive

In addition to that, cruise control failed, and pressing DTC button did not have any effect.

Having researched internet, I compiled a list of (more or less) possible reasons for that:
1. Weak battery
2. Flooded battery
3. Worn out alternator
4. DDE relay
5. LIGHT BLUE or SKY BLUE relay (BMW PN 61366915327)
6. Sensor module, located under front passenger seat (BMW PN 34526758750)
7. Faulty or dirty steering angle sensor (SZL)
8. Recalibrate the steering angle sensor (done via computer)
9. Reset the steering angle sensor (by turning the steering wheel all the way to the left and then right)

The most terrifying was #7 with expected bill of up to £1500. However, in my case the solution was none of the above.

Few days prior to that, I had MOT done which required track rod end to be replaced. I noticed that the steering wheel is slightly off-centre: to drive straight, steering wheel needed to be turned to the left. That was the reason.

It might have been possible to back off the track rod end by one turn, which would allow the wheel to realign.

However, I also needed front tyres to be replaced. Front tyres tracking (after replacement) solved the issue. As simple as that.

No warning messages since then. Cruise control came back, and DTC button behaves as expected. If this post saved your [day/night/life], my favourite beer is Hoegaarden