How to determine if PCV Valve or charcoal canister needs to be replaced?

It is highly unlikely that your PCV valve is going to ever fix a check engine light concern. PCV stands for "positive crankcase ventilation". It is basically a component that prevents pressure from building up in the crankcase to prevent engine backfire and oil consumption as well as other things. The charcoal canister is an evaporative emissions component -- completely different part / operation of the vehicle. Clearly, as you've had a smoke test, there is an evaporative emissions concern. Your PCV valve will not fix this. Might still be a good idea to replace after nearly 20 years, but it won't fix your concern. Testing by a reputable repair shop and technician is essential. www.repairpal.com/repair-shops