Haven't done an XC90 timing belt, but I did do my in-laws timing belt on a 2002 V70 XC and I did what you describe on it as well. Don't see why it would be any different on the '90.

The generic code readers will only read powertrain module codes... there are numerous modules on the OBD II bus, but unless you have a more expensive code reader, you won't be able to read out all the codes.