My friends 97 prelude keeps throwing a cel for knock sensor after running the engine for 15 minutes.Could this be a engine issue or just a sensor issue?

 

It's the sensor, the knock sensor CEL means that the engine can't find one, most likely needs to be replaced. My 4th gen did the same thing but luckily it was just the guy who helped with the swap had the wrong wires plugged to it.

 

The knock sensors are known to crack and break. and you are correct it wont immediately throw a CEL it throws it within a couple mins of driving.

 

Happen to know which other plug is the same as the KS one?

 

The oil pressure sending wire is similar and they are very close to one another. Its a blue/red wire on the 4th gens. I'm pretty sure 5th gens are a two wire knock sensor though.

 

It was the one for the air intake bypass, that black vacuum box beneath the IM, the plugs were the same.

 

thanks for the info i was worried it was reading somthing wrong with the motor

 

Na, if the knock sensor was working and doing it's job and there was something wrong with the motor you'd be getting misfire codes, the knock sensor code means there's something wrong with the sensor itself.

 

thanks a million