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Code 12 is for RPM signal and not the knock sensor which should be either Code 52 or 55.
It could be due to a faulty distributor or its circuits, starter circuits or a bad ECU. There are no diagnostic procedures for this code.
As to Code 28, it is a fault with the main O2 sensor and it could either be th right or left bank as pre-OBD II trouble codes are not specific.
I have emailed the diagnostic files to you. They explain how to go about cheking/repairing the problem.
Wednesday, June 9th, 2010 AT 8:25 AM