Engine is the standard 3.1 multiport injection, not the DOHC. Vehicle runs fine, only has 60,000 miles and gets good gas mileage.
The car failed the NOX emissions part of the Ohio test. Everything else, HC, CO, etc is nearly perfect. This points to the EGR valve, which is an electronic EGR (GM calls it a digital EGR). The valve itself seems fine, all three coils measure correct resistance and when individually activated as per the GM service manual, cause the engine idle to stumble as expected. I pulled it and cleaned it anyway, it was not clogged up.
So, the manual now says it is bad wiring or bad computer. Wiring seems fine and the voltage supply in the connector is fine, 12 Vdc. Can the ECM fail this way, only the EGR circuits not working?
Dennis