The Baum code reader book says about the round 9 pin diagnostic connector -

9-Pole Diagnostic Connector (1980-94)
The 9-pole Diagnostic Connector is used on earlier model vehicles. It can display
on-off ratio fault codes (1986 and later), RPM and Lambda sensor values. Various
on-off ratio Meters are available that provide access to this type of diagnostic
connector.

In other words your car does not have meaningful code reading ability. Even later 107s were primitive. You need a 129 body to have a worthwhile DIY code reading function.