I'm looking at fitting a decat pipe To my focus but from what I have found online I think it will cause eng management light to come on although I cannot find any more info as to why. Is this correct will it give Me a fault light? What causes this and anything that can be done to prevent it???

 

have a look on us sites sometimes thares better info thare maybe you have two lambda sensors and if you de-cat you may have to fool the ecu that the sensor is thare and still working

 

I run a decat on my ST, your engine light will come on due to the Lambda sensor sensing inefficiency of the cat (or lack of one). Remaps will cancel out the input from the sensor units