[e30lover318i]

Cheap fix is to put a “spark plug defaulter” in ..normally what happens is over a period of time the vehicle detects a cat efficiency issue due to a “worn catalyst” this is very common on the e90 chassis with n52 motor. The defaulter or oxygen sensor spacer pulls the sensor out of the flow to trick it into thinking it’s efficient. This is basically what people or companies do for the catted down pipes on the turbo motor, I’ve done a lot of cars with the spacer method but this boils down to your preference... some people get upset because it’s technically damaging to the environment... but any pre obd2 car is damaging the environment if you want to get technical as it’s not as efficient as the newer vehicles... hopefully this helps you I would highly suggest the spacer but you will need to find an Indy shop to do this for you as a dealer will NOT due it for liability reasons

Edit sorry didn’t read they are fixing it for you, please look into the n52 power e90’s for more info very common issue. Please be cautious with aftermarket cats sold to independents for example dorman has lower quality cats that dont always hold up