Check Engine Light And Cruise Control

[siddhartha]

ES 300 2003

My check engine light comes on. The code is related to the Knock Sensor. My mechanic (very trustworthy) says it needs to be replaced with the wiring harness (service = $900). Funny thing is, if I never put it in Cruise Control the engine light doesn't come on. When on the highway, and the engine light comes on while cruise control is enabled, and the engine downshifts going up a steep hill it then fails to shift back to OD, which I believe is a symptom of the Knock Sensor being bad. It is just odd that if i don't put it in cruise control it never does that. Does this mean my Knock Sensors aren't bad, but it is actually something with the cruise control?