code p0421

had this checked out by a good friend and her bf, great people. They scanned my car, and multiple codes popped up. one was P0421 and other p0660. Now P0421 is "DEFINITION-CATALYST EFFICIENCY LOW-BANK 1. EXPLANATION-THE OXYGEN SENSORS MONITOR THE CATALYTIC CONVERTERS ABILITY TO STORE OXYGEN. PROBLEM CAUSES- 1. CATALYTIC CONVERTER DEFECTIVE (FAILURE POSSIBLY DUE TO #2,3, OR 4) 2. ENGINE MISFIRE OR RUNNING CONDITION. 3. LARGE VACCUM LEAK 4. ENGINE OIL LEAKAGE INTO EXHAUST-VALVE GUIDE SEALS, PISTON RINGS. THE PCM HAS DETERMINED THAT THE WARM UP CATALYST EFFICIENCY FOR BANK 1 IS BELOW TRESHOLD FOR THE CURRENT ENGINE OPERATING CONDITION. (BANK 1 IDENTIFIES THE LOCATION OF CYLINDER #1, WHILE BANK 2 IDENTIFIES THE CYLINDERS ON THE OPPOSITE BANK)." A few repairs have already been done due to at first had random misfires, so far new timing belt, spark plugs, wires, ignition coils, full tune up pretty much.
So question to all, have you had this code yet, how did you fix?

So far thinking of replacing OEM headers with aftermarket but not replacing pre-cat. So i will go from 2 catalytic's to 1. That will be the mid pipe one will stay. What do you think?

Try replacing the o2 sensor. How many miles on your vehicle. O2 sensors usually good for 100k miles. Putting on an aftermarket header will now solve your problem. Infact it will give you another cel if you don't do the nonfouler trick to the second o2 sensor and even then it's not garuanteed

My car has 97000 miles on it, if I replace o2 sensor, and cel come back then I will do that header plus nonfouler at the other o2 sensor.

edit - I got a scanner, now i am down to 1 code. i guess i fixed something that i accidently came upon. Plus i cleaned the thottle body. Where can i get great headers for P5. once i get that i will get mid pipe and exhaust completely redone.

Let me get this straight, If you install a header, you need a non fouler in both O2 sensors? I thought you just need one on the first O2 sensor after the pre-cat (which is removed with my OBX header install).

funkytuqe said:

Let me get this straight, If you install a header, you need a non fouler in both O2 sensors? I thought you just need one on the first O2 sensor after the pre-cat (which is removed with my OBX header install).

Click to expand...

after the missing cat only. Once installed, no CEL, except for i switched to midgrade fuel, then back to regular, after that i had two CEL's, one for misfire and VTIC, i think it was. Erased them and am sticking to midgrade. No CEL so far. OH and car is gonna hit 100,000 miles here soon, 500 miles left. But car is still running like a champ!

funkytuqe said:

Let me get this straight, If you install a header, you need a non fouler in both O2 sensors? I thought you just need one on the first O2 sensor after the pre-cat (which is removed with my OBX header install).

Click to expand...

here is what mine looks like.

Ok yah, that is exactly what i have. Sorry i must have misunderstood. I am throwing a code now but i don't thin it's related, i'll just have to pull the code and find out.
This is mine:


Thanks!