Hello, I got this error a while ago and I & others can't find the "culprit". I have a Honda Accord VII '03 2.0 petrol (155 hp) 269000 km. At first the error (CEL - P0325) showed at 120 km done in one trip, after 2 days of standing in parking lot it turned off by itself, until the approx. 120 km done in one trip again. With time it showed up more frequent at the rate of a 5-10 km done. What I noticed is, If I delete the error and start the car after a few days "cold" the error shows after a few km, but if I run the car for at least lets say 100 km, turn off the car, delete the error then start again, after 300-500 m it back on. It shows up usualy when above 3000 rpm while in gear. If I turn on the AC the error pops up faster.
I've changed the knock sensor and harness with a aftermarket one at a Honda dealership ( they didn't have original one). Nothing changed, got back to them and after approximately 1 month and a half they could find the problem, the wiring was ok, no problemswith electrical. So I told them what's the worst problem it could have. In an instant they told me cylinder head and from there on they keep insisting on it, even after they run a compression test and the car passed it.
I took the car at other services and the mechanics told me not to open the engine, "the engine runs round" no knocks, no oil leakage, exhaust is "clean"(no oil in it)
I did a gas emission report to see if the exhaust system works as intended and it does. I did change the Lamnda sensor, the pre-catalyst one ( with Denso). I changed the accessory belt and belt tensioner. At the start it seems that this was the problem, that day I used the car around 20 km, above 3000 + AC and no light came one, but after 2 days of sitting around and after I entered (+30 km) the highway it came back on same error p0325. I changed the spark plugs twince now and the first ( 4 moths old) they look warned out

 

Those are probably not the correct plug. They look to be copper plugs and a Honda of your vintage runs laser iridium plugs. The high power ignition system will eat copper plugs in short order. NGK is the correct brand, just the wrong model.

If your knock sensor is not a factory Honda sensor it is suspect. NTK or Denso would be acceptable aftermarket replacements. Anything else is asking for issues. They also need to be torqued to a very specific torque to work correctly.

What market are you in? The US market did not get a 2.0 Accord. From my research it sounds like a euro market Accord with a 2.0 K series. If it is a European market Accord it would be more like the US market Acura TSX.