Hello, everyone, I was hoping someone on these forums could help me with a problem that has been plaguing me for the past couple of months.

I recently had the top half of my 99 Accord engine rebuilt after discovering burnt valves and low compression. It's a 99' LX 2.3L, F23a4. Ever since that job a new code has appeared in the P0235. Knock Sensor #1 - Circuit Malfunction (Single Sensor or Bank 1).
The mechanic had replaced the sensor twice after I showed the CEL coming back on after a short time. He said it was the ECU so I found a new ECU and flashed it at another shop thinking it would resolve my issue once and for all. Wrong. After about 60 miles the CEL came back with the same code. Now I have a perfectly good condition Accord with 116,00 miles on it that cannot pass NYS inspection due to a CEL that I cannot get rid of.
I have friends who have said the wire may be frayed, split, or something. Or the sensor/plug may be dirty. I don't want to go and start pulling things without possibly consulting with someone who has encountered a similar problem. Any guidance, advice or pointers in the right direction would be very much appreciated.

 

This is most likely the culprit.
Engine work done and now a code, most likely a wire/connection was strained/damaged.
Disconnect the sensor.
Check for continuity between body ground and PCM terminal C3
Is there continuity?
YES. Repair short in red/blu wire between PCM and KS connector.
NO. Ground KS wire to body and recheck continuity between terminal C3 and body ground.
Is there continuity?
NO. Repair open in red/blue wire.

Since you have already replaced the KS and PCM it is most likely a damaged wire.

Whomever removed the head probably damaged the wire when removing/installing the head and components.
Also Verify you are installing the KS to the correct torque specification.
Too tight can damage the sensor as well.