Thanks folks. I had already ordered the MAF and it got here this morning. I installed it and the the transmission light went away and the car shifts smoothly now. So, I cleared the MAF code using my cheap (bavauto SR 300-16) ECU code scanner.

However, after driving the X5 about 1 mile, I got the "Service Engine Soon" light, and reading the ECU yielded:

- O2 Sensor adaptation limit (1-3)
- O2 Sensor adaptation limit (4-6)

So, I drove it about 5 miles more and then the DSC, BRAKE and ABS lights came on.

I had replaced all 4 of the speed sensors about 5 months back, so I doubt it is the sensors.

How could I troubleshoot these two problems (O2 and the speed sensors)?