Check engine light NOT on during test period at start up
 

The check engine light lights up on all cars for a second or two when turning ignition key to on and then it turns off after that. Mine used to do that and now it does not. I check the light bulb and it works. What could it be? Thanks.

If the car is running okay don't worry about it. The main purpose of the CEL is to scare you into taking the car to the dealership and paying them a lot of money to make the scary CEL light go away.
The CEL on my 02 Cav has been ON for the past 15 years - I don't care. Car runs fine, I keep the oil clean, end of story.

Thanks for the reply but it doesn't work that way here. I need the light to function properly in order to pass smog check. If the check engine light doesn't light up when I turn the ignition on, it will fail the emissions test. And I need it to pass emissions in order to renew my registration. Does anyone have any suggestions please? Thanks.

In that case, I'd find a PCM (power train control module) at a junkyard, or borrow one from another Cav owner and see if that doesn't cure the problem. Buying a new one might also cure the problem. In any case, it sounds like the computer isn't getting or processing the info it needs to illuminate the light.
Also, try disconnecting the battery and leave it disconnected for 10-15 minutes, then re-connect it.

Thank you, I will briefly mention what I have tried... I checked the light bulb and it works when power is supplied directly to the bulb. I did swap the PCM from another identical year and model (2004 coupe LS sport) and that did not fix it. I have noticed too that sometimes, very rare, (ramdomly) it does light up the way its supposed to at start up but that's it, most of the time it fails. Could it be a ground connection not making contact probably? Where could I find the ground source for that signal? Thanks.

Oh yeah, I forgot to mention that disconnecting the battery did not fix it either because in one occasion, while trying to figure out the problem, I did disconnect and took out the battery for a day. It reset everything but did not fix the problem.

I suppose you've already cleaned the main grounds: 1 to the starter motor from the batt, and 1 directly to the engine block, also the one halfway down the negative batt cable to the bottom of the batt tray. After that, maybe get a wiring diagram and look for other grounds to check/clean.
Wouldn't hurt to ask a couple of professional mechanics for their opinions. There's someone out there who knows exactly what the problem is.

Ignition switch / ignition switch ground?

Thank you, I haven't tried checking the grounds yet because I didn't know where to start from. I will do that and update when done.

The black (ground) cable from the battery goes to the engine block. Remove it and sand/clean the cable connector until it is bare metal. After disconnecting the black battery cable, you can also remove the red cable from the starter motor and clean its contact area also. Corrosion where the cables contact the engine and battery can cause problems. Of course, the cable connections at the battery must also be clean.
The ignition switch may be worn out and in need of replacing.
The CEL light not illuminating is probably a common problem on all cars, so any professional mechanic should know what to check/replace.