well my buddies 08 civic si, he had a skunk2 exhaust installed by the honda dealership, and now hes got a check engine light. the dealerships only reccomendation is to put the stock exhaust back on, naturally, but thats stupid. and i contacted skunk2 and they said to check the wires to the sensors. the car is brand new almost, and when i scanned it with obdII its saying catalyst efficiency and 02 sensor. obviously this is a flow problem since the new exhaust allows more flow. there is already a spacer on the sensor, and i removed both of them and cleaned them, but the light comes back on. anyone have this issue, or know of any solutions? my only idea is software that will erase the code, but i kinda wanna know what the problem is if any of you ever experienced it. thanks for anyone that helps, this one is a puzzler

 

Fo you have a header on the car? Also get a defouler and that will clear it out. Take the terminal of the battery and let it sit for 15 mins

 

no header, just the cat back i believe, and i can clear the codes with the code scanner, the light keeps coming back on. whats a defouler?

 

defouler goes in the seconday o2 sensor spot before the o2 sensor its self. the defouler prevents the hotter air the exhaust is flowing (now) and makes the secondary o2 believe that the cat is cooling down the exhaust as it should be. It screws into the 2ndry o2 bung - the 2ndry o2 then screws into the defouler. ta da. no more cel

 

ahh we call these o2 sensor spacers in the vw world. no hate intended here, but id like to thank you for your help. im now educated. while i was under there i noticed what looked to be a defouler, but it was on the first bung, closer to the engine, and it was like a 90 degree angle. idk if this was to accomodate the sensor with the larger diameter pipe and keep it from hitting the floor, or if the dealership that installed it just put it on the wrong 02 sensor. so its supposed to go on the rear one? if i dont have enough room when i take it off the first and move it to the rear sensor, would there be problems still if i just put an additional one on the rear and let the one on the front? sorry for the million questions, i just wanna get it right.

 

Aren't both O2 sensors located on the header? If he doesn't have an aftermarket header installed then how would an exhaust trigger a cat cel? The secondary O2 sensor is there to ensure that there is a functioning cat. converter.

 

I honestly cant remember. I havnt had a cat on my car for over 3 years