code P0325

I have had driveability problems for a long time with my '97 2.2 Cav (stuttering & stalling). Finally, a friend diagnosed it as a ECM computer module the was not functioning. I bought a rebuilt, pre-flashed ECM and installed it. I performed the anti-theft re-learn and the vehicle runs great!
A short time later the check engine light came on. A-Zone read the code
as P0325 (knock sensor). They also mentioned that there is no way to test the sensor, but for about $30., they would sell me a replacement, that may or may not solve the problem.
Could anyone please tell me where the sensor is located?
It seems odd that there were no codes with the old ECM, but codes almost immediately after installing the new ECM.
Any advice will be greatly appreciated.
Thanks,

Things can go bad at any time, may have gone bad with the old pcm too.

You can check with a Tech-2 scan tool to see if it's bad... but you probably don't want to spend thousands on that...

Just check that the wires to it are good, every time I've seen that code it's been the knock sensor itself. The code sets when there is no voltage from it, it's a crystal that generates it's own mV. Should have a "vibrating" voltage if you can check it with a volt meter.

Knock sensor location:

Back side of the engine block right next to the Camshaft Position Sensor (CMP) by the exhaust manifold.

Also, for the record, there is a way to test knock sensors... you need two things, a multimeter and the circuit resistance rating for the sensor. Essentially, buy an new knock sensor, test the resistance, then compare to the old one. If the same, KS is not the problem.