Quick question here, what do the lambda sensors in the turbo downpipes do? I have a cat bypass pipe on my 32 and therefore the cat sensor is disconnected. A Nissan diagnostics was done (by a reputable source) and showed both lambda sensors to have no reading. I was advised to fit new ones as they will affect the performance of the car (I am doing a dyno day soon). My mechanic is under the impression that the lamba sensors need the cat. Is he right or wrong. Any advice gratefully received as new sensors should arrive tomorrow.