obd1 ecu won't scan w/ a scan tool even if it's in an obd2 chassis. you need to find the svc/jumper connector which either be behind in the passenger side kick panel area (civic/integra) or behind the center console/ashtray area accord/preludes. if it's an obd2 chassis accord/prelude w/ an obd2 scan port then you can also jump 2 of the pins on the scan port, but i forget which 2.

best bet is to google this depending on what you have...honda-tech.com also has something somewhere on it too, but you'll have to search for it.