2000 Other Jaguar Models Check engine light turned on after

Engine problem
2000 Other Jaguar Models 6 cyl Wheel Drive Type unknown Automatic 90000 miles

Dear 2 carPros,
I like your videos and repair pictures. I think you are the only one out there doing this. My problem started when I used water with some soap to clean my engine in a Jaguar 00 S-type Auto. I was hoping to save money by not using the steam wash from my local war wash. After I cleaned and wet my engine, my engine's "check engine light" turned on and it now roughly idles. This actually happened before, and I know that my mechanic changed a sensor which worked ok. I want to know what kind of sensor is that and where is it located. My mechanic charged me a lot from that incident. I hope I can repair it myself.
Thank you and more power to your web,
Peter