Check Engine Light not working?

My '97 GMC Jimmy 4x4 SLT with 130K miles failed a recent smog test. The tech said the computer meters all fed zero and the "Check Engine" light on the dash would not light up; which I validated by turning the ignition key to "On". The only recent service I've had was replacing the ignition switch in the steering column; which my local GMC dealership did. Other than failing the smog test, the truck runs great and would have passed. The rest of the idiot lights seem to function correctly and I can't identify any other issues, mechanical or electrical. Any idea what would cause this problem?