No this is not "i want to burn my car to the ground" thread. Ive wondered if my knock sensor is working correctly. I took a hammer and tapped on the block with the car running and nothing showed up on the laptop. Shouldn't this work and show up as knock on my datalogs? Would i get a code if it was broken? Any way to check besides this method?

 

The knock sensor may pick up hammering on the block, but I would imagine it would depend on how hard you hit the block and where you hit it.

To answer your question here is a detailed explanation as to how to test a knock sensor:

http://shbox.com/1/4th_gen_tech2.html#knock_sensor

 

unless you can create the frequency the knock sensor is looking for, you are only needlessly beating the crap out of your block with that hammer

 

Lets say the sensor is bad. What would it do to the cars performance? Would it cause something like a limp mode since it can't detect knock? I will check it as soon as i have some time.

 

The PCM just checks the voltage on the knock sensor circuit. If the voltage is not within the specified range (1.5V - 3.5V), it sets DTC 43, and the PCM calculates knock retard from other engine operating parameters, resulting in almost constant knock retard, ranging up to 15-degrees. You can check the electrical cirsuit using Shoebox's guide. Note that the 5.0V reading is to be measured with the harness wire disconnected from the KS. That verifies the reference voltage from the PCM. The KS resistance should also be measured with the harness wire disconnected. Then reattach the harness wire, and probe from the single wire/pin on the harness/sensor, to the block. That is the value that should be in the range 1.5V - 3.5V to avoid setting the code.

Since its only checking the voltage on the circuit, and hence the resistance of the KS, its not going to detect certain failure modes. I saw one case where a piece of RTV in the water jacket had screwed up the sensor.

As noted above, the piezo element of the sensor is "tuned" to the specific frequencies that the GM engineers feel represents detonation. It might not pick up all known frequencies.

Your PCM may revert to some default programming, but it seldom, if ever actually reaches the state of being in true "limp mode".... that is a mode that results from the PCM having lost almost all of the possible inputs, and its doing whatever it can to somehow keep the engine running. "Limp mode" is an over-used term.