Rallye lambda sensor, eml light?

[Mitch]

My rallye has an aftermarket exhaust system fitted, from the manifold back, there is no lambda sensor fitted in the system at all, the plug is just lying loose by the bulkhead! was wondering if the eml light should be on? as it isnt and never has been? i tried to read the fault codes at work but our diag wont read it! surely the light would be on if there was no signal from the lambda?!