Code Reader Not Reading Fault Codes

[Glyn84]

I've always had a few check engine beeps on my 6L Monaro from the lambdas but I'm getting ones now which I don't think are related. The last time the codes were read at a garage there was other stuff in there too, so I've decided to do something about it and see what they are.

I bought the Sealey VS8801 code reader (http://www.ebay.co.uk/itm/SEALEY-EODB-READER-WITH-LIVE-DATA-VS8801-BRAND-NEW-/281148466507?ssPageName=ADME:L:OU:GB:3160) which was recommended on here for the Monaro and also for working with pretty much everything else too. It seems to connect to the car OK and passes all the initial checks, can read rpm etc but it always without fail just shows no fault codes, even when the check engine is beeping away merrily.

Have I missed something here or doing anything wrong?