The good news is that the service engine soon light is on and there are stored
trouble codes in the ECM (engine control module) which can help guide you or a smog technician to the location of the engine problem. The OBD-II problem the smog tech is referring to probably relates to your Astro van's emission monitors. Emission monitors are internal self-tests which the computer performs and check-offs indicating certain emission systems are functioning properly and the vehicle is ready for a smog inspection. With the service engine soon light on, it is very possible that one or more emission monitors are incomplete. Making them "complete" or "ready" for the smog inspection will require you first take care of the service engine soon light problem and then drive your Chevy Astro van through a GM drive cycle in order to complete the monitors. So first thing to do will be to purchase an OBD-II scan tool (if you don't have one, you can buy an inexpensive Trouble Code Scan Tool from any auto parts store), and pull the trouble code data from the computer. The trouble code will start with a "P" and be followed by 4 digits. The trouble code will tell you which part of the engine's emission system is defective or damaged. Once the location, component or system is identified, you may then diagnose the particular problem.
