Engine Light on PT Cruiser 2008 will not turn off

I have a PT Cruiser 2008 with 52,000 miles.  For the past 2 years, the light
stays on and give the same code of misfiring cylinder.  Have taken it 3 times
to the maintenance shop - first time they read the same code as I had, did a
tune up, but the light came back on after 200 miles.  Second time (less than
two weeks after tune up), they read the same code and said the firing is fine.  
Have had two emission tests since this started and I pass with flying colors.

I take great care of my "Cruise" and check the code each month - same code
over and over again.  Have no problems driving the car and it does not give a
physical indication that any cylinder is misfiring (around town or on the
Interstate).

I can clear the code with my reader, but it pops back on.  Any idea what can
be done to reset (re-program) the engine light software?  Maybe something
else?

Thanks ahead of time for your review and assistance...
SL PT 2008