My 2009 mini cooper S has the trifecta of warning lights--ABS, Brake, TSC. I get error code P1774 suggesting left rear speed sensor is the problem. Here is what I did:

1. Replaced speed sensor. Did not fix the problem.
2. Checked voltage at speed sensor connection--500mV! Traced wiring back, found frayed area, cut out frayed area, soldered back together, covered with heat shrink and tape.
3. Confirmed voltage--I now have 14V at the speed sensor connection (although it does bounce around by about 100mV). But problem not fixed.
4. Removed right rear speed sensor and put it on the left (no speed sensor on the right at that point). Now I got P1774 and P1775, indicating both speed sensors were malfunctioning (the P1775 was expected, because there was NO speed sensor on right at that point).
5. Put left speed sensor back on the right, and the left speed sensor back on the left. Now back to just P1774.

So it seems that the problem is not the sensor, but is upstream. Does this mean the problem is likely the dsc control unit? Any other diagnostics I can do to nail down the problem?

Thanks!
Eric

 

May not be related but worth checking:

brake fluid?
do you have NCS expert to try to recode it?

after the fixes, did you try to drive the car so the ABS module can update the values? or can you look up the live data to see if you're getting any readings?

 

Thanks MiniToBe for these ideas! Brake fluid level is good. I do not have NCS expert, but I am able to clear the P1774 and P1775 codes with my bosch code reader. Unfortunately, the P1774 keeps coming back. And yes, I did drive it after "repair" and still no joy.

I am taking it to the shop tomorrow. I will post back here with any findings. Unfortunately, though, this ten year old mini is wracking up the expenses at an alarming rate so may not be with us much longer =(.