The knock sensor that suddenly went deaf

Sigh, they just don’t build em like they used to do they? Case in point the knock sensor I installed roughly a year ago that suddenly seems like it’s suffering from hearing loss..

Luckily these things are pretty easy to test.

The warning signs appeared..

The on again, off again, on again some more, then away for a couple of days and then on again check engine light is always fun to see. As is your fuel tank chewing through things far quicker than usual. But I think the most annoying part of all of this is that this particular knock sensor had the laziest life of all time (I’ve barely clocked up the kms in this thing, especially when the head gasket failure signs started to appear) and still decided to hang up its wires in under a year.

But before ordering in a new one, we may as well check that it is the knock sensor in this case causing all the issues (even though the onboard diagnostic mode is certainly waving a digital finger in its direction.)

How to test your knock sensor

  1. Firstly pull it out. And if yours is in an 2005 Impreza or so, then lucky day, here’s a handy guide on installation (just read it backwards for removal I guess.)

2. Break out your multi meter. For basic car stuff like this, I used a pretty basic model that covers all the usual stuff including volts, amps and continuity which I grabbed yonks ago from Supercheap Auto.

3. Get ready to actually ‘knock’ your knock sensor and see what reading you get. Taking a photo of me attempting to do this would be problematic given I have only two hands and no assistant, so instead let’s refer to my new friend Aaron here who showed me how it all works (his video is perfect for any single wire knock sensor like mine seems to be.

4. This is one test that you can do but I looked into a few others for peace of mind. So a shout out to Mr Fix It who explains here how to check for continuity, voltage, ohms etc. Which tests should you do to check your knock sensor? If you’ve got the time, I’d suggest all of them really. Then you can prepare your funeral rites if necessary.

She’s not dead, but dying

The knock test didn’t rate well for this one, I couldn’t get it to register up to a volt tapping away with a socket. Other tests showed that while there’s some life in the unit, the measurements really aren’t up to where they should be. So I guess this motor microphone is hearing something, but not performing within spec. No wonder the Slowbaru has been having some rough days as of late!

Time for a new one then! (Let’s hope the next one lasts a lot longer than this one did!)

Knock sensor quick update

After testing it and giving the circle where it meets the block a quick wipe down (it had a bit of grime forming up on the outside of it) I reinstalled it and then went in for a cup of coffee and to order a new one. Coffee was good but I got distracted by something (more than likely my kindle) and clean forgot that last part.

And after the first three days of no check engine lights, I thought maybe I was lucky enough to sort things out – maybe unplugging it and plugging it back in was all I needed to do!

Er no. CEL back already. Business as usual then and time for a new one.

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