Fail codes p0325 and p0135 but check engine light won't come on.

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I took car for smog test and it passed all requirements but an exhaust leak at one of the exhaust manifolds. Emissions passed with flying colors. Smog machine did not read fault codes.I removed manifold and replaced 3 broken studs and replaced the gasket. Put it all back together. Took van to smogg and the machine returned fault codes but mechanic was puzzled that engine ligjt wouldn't come on with the engine running. My scanner pulled a p0325 for knock sensor and p0235 for sensor heater malfunction. Any suggestions?