I think you will find that the cam sensor on these are inductive type so there you should be able to read 2 resistances.With plug disconnected and ignition on I think the voltage is around 1-1,5 volts.The hall effect sensor can be found on the 2.2 engines fitted to Omega models which run a different management system.If you have access to Bosch esi.all the info is available here.Also does it have the modified sensor and adaptor wiring harness?