Rickford

This thread has been around for awhile but I'd like to add something. I have a 2007 with a bad knock sensor. Everything I've read or watched on youtube shows replacing from the bottom. I don't know if there was a design change on later models but I just changed mine start to finish from the top. No jacking up and crawling under etc. Was it a bitch? It sure was! Was it easier than going under? yup again! Are my hands a little nicked up? yes again, but it's still easier than from below. What added to the trouble was the fact that the green connector was broken off the sensor. Getting that out of the black plug was really hard. I rerouted the wire up and over the harness it comes out of and thus was able to get a better grip on the release tab and got it off. The rest is straightforward, 24mm socket, 1/2 to 3/8 adaptor, two short extensions and, if you have it, a flex head ratchet. I could not get mine to release so i used 3/8 breaker bar to break it loose. It lets go all of a sudden so be careful! Removed and installed by hand after that. Couldn't begin to know the torque but it was really tight. I just used the breaker bar again. After it seats there is absolutely no play. Using the breaker bart I felt no movement but put some muscle on it anyway being careful not to move the socket off the hex which would break the green plastic off again. If you do...go to step #1 Hope this helps somebody!

S2K-OED

I too had to go in from the top. It could've been done from the bottom but I had very little room in my garage to have been able to position myself under it properly. Also from the top (once intake manifold is off) you're able to see better what your doing with such an expensive and fragile part in your hands.

ODJob

Managed to remove this wee blighter accessed from under the car and removed the front left wheel to get access with one arm each side of the engine mount.
I did need a short extension on the 1/2" socket as shown on the picture attached. Very tight and when it gave way I thought the socket had come off but to my relief the sensor was loose and easily removed by hand. Now looking at the Ballade sport replacement...
Had to use a flat bladed screw driver to remove the plug from the top of the sensor which had detached itself from the body.

S2KEEDIY

Just some information for the thread:

99-10 Odyssey PN: 30530-P8F-A01
Resonant Frequency: 11.6 kHz

00-05 S2000 PN: 30530-PCX-003
Resonant Frequency: 14.5 kHz

06-09 S2000 PN: 30530-PRC-003
Resonant Frequency: 11.1 kHz

I would not suggest using the Odyssey knock sensor for your S2000.

Also, I have not seen any mention of the torque spec: 23 lb-ft

Slowcrash_101

Resonant frequency is not the same as the knocking frequency, which is similar enough for each knock sensor to pick it up.

S2KEEDIY

Why would Honda have 2 separate part numbers for 2 different resonant frequencies in the exact same housing? Not arguing, just discussing.

From what I understand, there are 2 basic types piezo knock sensors (resonant and non-resonant). Ours is the resonant type or "narrowband", which is tuned to a specific application and can only detect a certain frequency of knock.

Slowcrash_101

How does knock happen? Gasoline pre-ignites, or detonates, which sends a shock through the motor, a knock is orders of magnitude higher than anything the engine does under normal operation(around 75hz). Thus the knock sensor is tuned to listen for an abnormally large value. The Honda Odyssey knock sensor is designed for an engine that's made to run on 87 octane and thus has a gasoline that's more prone to pre-ignition thus you specify a more sensitive sensor.

The S2k runs on 91/93 octane, the fuel makes it less prone to pre-ignition, thus has a less sensitive sensor. The DBW S2k has a more sensitive sensor because it operates more "on edge" than the cable throttle versions. The specific frequency isn't the trigger, it's any frequency that is at or higher is treated as knock.

Pre-ignition can have several different frequencies depending on when it happens during piston travel, and valve opening. The damaging pre-ignition has a frequency limit.

The only downside to using a more sensitive sensor on an AP1 non DBW AP2 is that things like heat soak will affect you more in terms of hesitation. In other words you're not going to damage the engine, in fact it'll be better protected at your annoyance when you need to show off your speed pulling out of a parking lot.

Lugging the engine at low rpm, ie flooring it at 2k rpm has a much higher chance of causing knock than full throttle at 8k rpm. Where the less sensitive sensor may let you get away with it to an extent, a more sensitive one will cut power if it hears knock, but once the IAT's go down it'll restore your power and off you go.

Fun fact, humans can hear from 20 - 20khz in terms of frequency which puts engine knock frequency somewhere in the upper half.

Soviet

Hey folks, I made a video about this DIY that I think may be a little more approachable than the OP's description since it helps visualize what is going on.