JimF, there are two sets of codes: one for the Impusle Counter Scan Tool and the other for the Handheld Tester (HHT).
For example HFM code 13 refers to O2 system at limit (ICS code)
HFM code 35 O2 system operating at rich limt, mixture too lean (HHT)
HFM code 36 O2 system operating at lean limit, mixture too rich (HHT)
HFM code 84 Momentary fault in Self-Adaptation of closed throttle speed/partial load (HHT)
As you can see, HHT provides more information.
www.alldatadiy.com is a good source