Hello, I have Porsche Cayenne 2011 and the 4ABS FAILURE, PSM FAILURE, FOUR WHEEL DRIVE massage is on display. I had it test with the computer and is the front left speed ABS sensor. My question is, is t needed to change all 4 ABS sensors or if I change just the front left will be ok

No you just need to repair the defective one...

I agree with Joemom above. The other sensors should be checked for debris build-up around them. In fact, you might try removing the front left sensor (easy to do) and try cleaning it. Spray some electrical contact cleaner on the plug in connectors while you're at it. Good luck!

My 2011 Cayenne diesel just happened the same problem w/ yours. Did u solve the problem? How much did u cost? Where to find the parts? Many thanks~