Failed CA Smog because of OBD self test non-completion?? 2003 Sebring Sedan 4 cyl.?

(I have my own OBD and it worked fine 3 months ago. - actually it showed a code for a sensor, so I took the car to Pep Boys where they wanted to do their own thing. They hooked it up and came up with a new code I had never seen, then replaced the sensor my code said and it has been fine since) * * * Now I do a smog cert and the car fails because "..failed the MIL/check engine light due to failure to successfully complete all OBD self test." Now the test-only station says to go to the dealer but they want lots of money to even look at it. - any ideas why it would not complete all the self test successfully? (2003 Sebring 4 cyl, 66K miles - car originally from Texas)