[5_LiTeR_EaTeR]

First off you want to make sure you didn't stripe it out, that what it sounds like in your case. you only want to torque it down to about 7 ft lbs basically just snug it. If you wrench on it like its a tranny bolt then you will end up ripping the threads out cuz they are very fine and is aluminum. You probably won't be able to take it out. If you can't take it out get a screw driver and pry it outwards while turning the sensor. That will enable you to catch some of the threads that are left and make it possibly for you to take it out. Second code 23 is the knock sensor. Either the knock sensor is faulty(but isn't cuz you replaced it but doesn't mean the new one isn't bad) or the circuit to the knock sensor is shorted or open. Basically what you want to do is is check for continuity from the ECU pin to the knock sensor itself. Disconnect the battery and uplug the ecu connector with the knock sensor pinout. take a volt/ohmmeter and see if you have continuity from the ecu plug and use the other side of the ohmeter to the plug to the knock sensor. if you read anytihng you should be okay. it should read .00 to .02. Then make sure the pin to the ecu hasn't bent or any of the connectors has been messed up like a connector coming out of the plug itself. Thats basically the troubleshooting for the sensor. It is common for the ECU to throw a code and not have the MIL light come on (Malfunction Indicator Light - check engine light). What it means is when it throws the MIL light on the ECU will make the car run in a limp mode or diagnostic mode. If the MIL light comes on it means there is a fualt in the powertrain system but will not effect driveabilty. I hope that helps Good Luck.

~Alex~