I replaced the stock dual catatlytic converters with a single Magnaflow. Previous posts state that if I do this, the CEL should come on, because it is not reading two cats. How long should I wait to see if the light comes on? I drove the 4runner yesterday after the new cat was on, and the CEL has yet to come on. Previously, it took approx. 2-3 weeks before the light would come on after resetting it. The code was for the bank 1 cat. Also, I had a head gasket leak, that was repaired, but the damage was done to the first cat., hence the CEL.