The knock sensor for my 2001 Subaru Outback grounds through the engine block. I've seen various advice about whether to put dielectric grease on the underside (where the grounding takes place). Some say 'no' - it will add resistance to the ground path, others say 'yes' - the resistance is negligible, and it will help prevent corrosion.

So my question is: is it recommended to put dieletric grease between the knock sensor and the engine block? And why?

For context: I replaced the knock sensor 1 week ago, and I used dieletric grease. Seemed fine at first (no CEL, no OBDII codes), then today the CEL came back on with code P0328.

  • What was your original reason for replacing the sensor?
    – jscs
    Mar 12, 2015 at 21:18
  • The original reason was a P0328 code - sorry, I forgot to mention that.. The one I removed was cracked.
    – tom
    Mar 12, 2015 at 22:14
  • I doubt the dielectric grease would create any issues to it grounding. I'm wondering if there might be something else going on here where the signal isn't getting back to the computer or if something else is causing the problem in the first place. Mar 13, 2015 at 12:15
  • Sounds plausible. Perhaps the ground path from the engine block to the battery? Though that would probably affect other things, right?
    – tom
    Mar 13, 2015 at 16:55
  • I'm wondering if it is in the wiring connection to the sensor (ie: the sensor plug). Have you checked for any corrosion on the plug side? If none, check the wire back as far as you can. You may also be able to figure out which pin it goes back to in the PCM connector and do a continuity test to there to see if there is any issue in the harness itself. Apr 25, 2015 at 13:49

1 Answer 1


Knock sensor is just acoustic device. Any materials between it and block will distort sound and signal. If you asking about wiring ground point - it is also doesn't influence on anything. So, my opinion is ignore grease. Hope I understand you correctly.

Good luck!

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