Replacing knock sensor - dealer?

[Preston Brown <pbrown@econ.yale.edu>]

I have to have the knock sensor in my car replaced.  The fault code of 
the ECU indicates that either it or the wiring is to blame.  I think I 
recall that someone in the past week said that knock sensor was approx 
$50 from Clair or some place similar.  I am sure that my dealer will 
charge more, correct?  But how do I know if it is the sensor or the 
wiring?  I should probably take it in and have them evaluate the 
situation, and if it will cost substantially more than $50 for the part, 
I should buy it and then have them install it, correct?

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 -Preston Brown
  preston.brown@yale.edu