ABS and Traction control light fix.
My 2001 P38 had the ABS and Traction Control light come on a few months ago. It would stay on all the time and when I first started up the car the display panel on the speedo would flash abs failure and traction failure. I tested all four sensors with a voltmeter and they all tested fine and were set to the proper length. I went under the glovebox to access to the ABS ECU to see if any of the cables were damaged. I unplugged all cables and it looked fine. I put everything back together and when I started the car the lights went away, but after driving for +10 miles they came back. Curious I disconnected the battery for a few minutes and plugged it back in. Again the lights went off but after 10+ miles of driving the error lights were back.
I know some of you might not have access to a testbook but a local shop in town ran it for me free of charge. The error codes were
REAR LEFT SENSOR OUTPUT TOO LOW
REAR LEFT SENSOR SHORT TO ANOTHER SENSOR
The tech had no idea what would cause this other then the rear left sensor had to be bad, but I was %100 sure it wasn't. Out of options I got a spare ABS ECU from a yunk yard for $40 US and plugged that in. The lights have now been off for 200+ miles.
So, if you have those 2 lights on, you know your sensors are good, it might be worth changing the ABS ECU.