I have a 1998 Outback wagon, 2.5L, 157K miles.  My CEL is indicating P0325 so I ordered a replacement knock sensor.  I removed the old one (housing is cracked), installed the new one, turned the key, and...just a click (the single starter click).  The new sensor is oriented correctly -- it's not resting on the hump -- and is not overtightened.

 

I removed the sensor, reinstalled the old one (the car did run with it, just had hesitation during acceleration), and...same problem...just a click.  I measured both sensors on my multimeter using the "2000k" ohm setting.  The old sensor reads 553 and the new one reads 552.

 

What the heck could be wrong?  There doesn't appear to be any corrosion on the engine where the sensor bolts down.  I checked all nearby connectors and nothing is loose or disconnected.  I even removed the negative battery cable for 10+ minutes to make sure everything is reset...no change.  The car just won't start.  Could I have blown a fuse?  Which one?  I'm really at a loss here...

 

check battery connections or starter is the engine turning over?

Welcome to the USMB, vulture! 

 

I doubt that your knock sensor and the no-start situation are related.  Make sure your battery posts and the cable clamps are clean--and that the cables aren't corroded at the clamp connections.

 

If they're okay then check the copper contacts inside the starter solenoid.  They often pit and wear, keeping power from getting to the starter motor.  Installing new contacts is a relatively cheap and easy fix.

 

Good luck!

will the car jump start?

 

also, if this car has seen a lot of starts/stops in it's life, the starter could need solenoid contacts - easy rebuild.

Just a conicidence. The knock sensor doesn't have anything to do with starting or the starter.

 

Bad battery connection or the starter solenoid contacts are worn.

Thanks very much, guys.  I have a battery terminal cleaner and used it on the posts and cable ends.  They didn't look bad and I was pretty sure the battery was making good contact, but cleaning it seems to have done the trick.  It's starting reliably now with the new knock sensor installed.  What a weird coincidence.  I'll also look at the starter solenoid contacts.  Thanks for the tips!