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Originally Posted by b3lha
The service manual says that when you get Code 22 then you should check the knock sensor and it's wiring. The resistance of the knock sensor should be approximately 560k Ohms. The wire should be at 2-3 volts when the ignition is on. So that is absolutely the first thing to check. I'll add some further info from my personal experience. But take it with a grain of salt because I can't find anything to support this in the service manual.
The knock sensor detects vibrations from the engine that indicate that it is knocking. When the ECU gets a signal from the knock sensor it retards the ignition timing until the knocking stops.
Some time ago I picked up a load of really bad fuel in my 94. The car wouldn't run on it. I had to drain the fuel tank, but obviously I couldn't get every last drop out so there was still a certain amount of bad fuel mixed in with my first tank of good fuel.
For that first tankfull, I was occasionally getting codes from one or other of the knock sensors. I think that the engine was knocking due to the bad fuel. The ECU was retarding the timing to try and stop the knock, but the knocking didn't stop so perhaps the ECU decided that the sensors must be bad. It wasn't obvious to me that the engine was knocking. It just sounded maybe a little less smooth than usual, difficult to say for sure. After the next fill up everything was OK.
In summary, I think another possible undocumented cause of this code is that your engine is knocking due to fuel/timing issues and the ECU is assuming the sensor to be bad because it cannot stop the knocking.
If the knock sensors and their wiring test out OK then try filling up with premium fuel and resetting the ECU.
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I would take that said with a lot more than a grain of salt. The analysis is logical and valid.
The knock sensors contain a ceramic element and are quite fragile in respect of heat and age, so that failure must be suspect.