No trans code either? A trans code can trigger a check engine light.

You can try a used ECU if nothing else to see if that's possibly your problem. The reason why you might not be able to do what someone else has suggested, putting tape over the light is because in some states now, like mine, they test all '95 on up cars by using a scan tool only so if the light's on, I'm sure they'll fail you until it's fixed.

If you're having a dealer look at this, ask them if they'd try another used ECU from another '95 850? It's very easy and I've done that at times as it'll take further guesswork out of it and no parts department wants techs or customers returning costly SOP electrical parts either. There's no way any tech can test a ECU as all Volvos diagnostics test everything but, then one's left to assume it's an ECU problem. They're not that expensive when found used, a fraction of new part cost.