So i want to get a grimspeed up pipe but ive heard that WRX's need to have 2 CEL fixes. 1st Fix CEL code P0546 = Exhaust Gas Temperature Sensor Circuit Malfunction (High Input) with a 2.2k 1/2 watt resistor to the EGT connector. How would you be able to be the other is rear CEL code P0420 Catalyst System Efficiency Below Threshold. I dont want CEL, i want 2 for 2! and fix both.