"Service Engine Soon" light on

[theG35spot]

I have a 2004 G35 coupe and installed an MREV2 on Nov. 4 and a Greddy EVO2 exhaust on Nov. 5. About two weeks later, my Service Engine Soon light came on. I thought maybe I just needed to reset my ECU so I tried the pedal reset method about 20 times very carefully and it didn't work so I disconnected the negative battery terminal and pumped the brakes. That turned off the Sevice Engine Soon light for a couple of days, but of course it came back on. Also, during these couple of weeks my car stalled two times, both while I was driving on the freeway, exiting on an off ramp while down shifting.
I went to AutoZone to use a scanner to check the error code and the code came up as P0455: EVAP Emission Control System Leak (Large).
I checked my gas cap and it was on tight with multiple clicks, then I took my car back to Auto Innovations where I had the Greddy installed and they checked everything over and everything was in place.
I assume that the problem has to do with my EVAP control box, which was relocated to install the Greddy exhaust, and the sensors got messed up in the process. Can anybody confirm for me if it is the exhaust? I'm just trying to narrow it down to one or the other, the Greddy or the MREV2. I don't want to have to put back both the stock intake manifold and the stock exhaust if I don't have to. Any feedback would be greatly appreciated!

[Gilley]

If they relocated the evap cannister, that would be the first place to check for a problem.

Also, make sure your gas cap is on tightly.

Have you had the recall done for the fuel filler hoses? They could be cracking, which is what the recall was for.

[theG35spot]

The gas cap was the first thing I checked because everybody told me that is the error code you will scan if it is not on tight. It seems to be fine.

My installer thoroughly checked all the hoses and connections to the EVAP box and everything was fine, so we don't know what is wrong. I think it's possible that the sensors got messed up when they relocated the EVAP box.

I believe I've gotten the fuel filler hoses replaced, but I'm not sure. I had a big problem last year filling up my gas tank. The car would only allow me to fill maybe a couple gallons into the tank. At first I thought it was the gas station I was going to but after trying multiple gas stations I realized it was my gas tank. After a couple trips to the dealership it was finally resolved.

If nobody knows exactly what the P0455 error code relates to, I guess I'll have to put my stock exhaust back on and take it back to the dealership so that they can fix the EVAP control sensors?