Code P0421

[mrg7243]

Well I did a ricer thing and gutted my pre-cat on the galant 4g64 of course, I finally got rid of all the exhaust leaks, and I was 670 miles code free, and then it popped up today. I did the spark plug anti-foulder trick, when I first did it. So what do i do now?? is there another trick I have not found?? I know there is the resitor trick, but I cant figure that out if someone could please help.

[mko]

This is the schematic. You dont have to do all of it since you have a working 02 sensor.

Just use half of it - the capacitor and 1MOhm resistor. I cut the 2 wires that are for the signal and ground and splice this instead. IDK where the rear o2 sensor harness goes in the body, but for 7g is right under driver's seat. Thats where I did it and tucked it away in the center console. Leave the heater wires alone. Just find out which wires are for the signal and signal ground

[mrg7243]

alright thank-you, seems simple enough off to radioshack this weekend

[djhah]

So I have the same code but have not done the anti fowler trick should I do this before I try the resister trick?

[mrg7243]

So I have the same code but have not done the anti fowler trick should I do this before I try the resister trick?

i would, it wouldnt hurt to try. I was code free for almost 700 miles with them.

MKO is this the right wiring set-up, i just mocked it up to see if it is right before i go fully wiring it.

[mko]

yeah, you can bring the resistor up to the capacitor pins and wire it from there

[01sedan]

i did the capicator and resisitor trick on the blue and white wire but left the heater wires alone the check engine light still came back on my car is 01 with 232 XXX on it and gutted pre cat also do you think i need to add resistor to heater wires or but replace main cat down stream o2 sensor i know the rear o2 sensor is black sooted up i clean with wire brush and help appreciate

[Isaurio]

Change the o2 on the pre-cat. If that doent work. Get headers or i have a extra precat for the i4

[01sedan]

i have already changed o2 sensor on pre cat before i gutted it but if rear o2 sensor black soot that mean that o2 that having problems correct i was just wondering can move rear o2 like you did on your car to behind main cat

[mko]

do the electronic fix and the mechanical fix. Get a spark plug fouler (2 in a package) from pepboys and drill one of them out so you can bolt in the O2 sensor.



and then do this

[Conjee]

I had the same code, P0421 a year or so ago. Did the mechanical fix above and have been light free. Passed inspections, right after, then passed it again the next year. As of today it is still on it and no lights. I used part # 42009

[Isaurio]

i have already changed o2 sensor on pre cat before i gutted it but if rear o2 sensor black soot that mean that o2 that having problems correct i was just wondering can move rear o2 like you did on your car to behind main cat

U could do that but is not going to make a different. When u change o2 is a good idea to change all of them. Before u go crazy and start changing things. Change the other o2 and see what u get also reset ecu so it could re-learn new readings.

[Brian03Galant]

anyone have a pic of this installed on the car. My CEL keeps coming on amd going off with same code everytime. The resistor method I mean

[spdracr]

Replaced the precat o2 and light didn't go away. Originally bought 2 o2 sensors and was just too lazy to replace the second one. Gotta get on it soon.

[Galantic]

do the electronic fix and the mechanical fix. Get a spark plug fouler (2 in a package) from pepboys and drill one of them out so you can bolt in the O2 sensor.



and then do this

Thank You!!!! The spark plug fouler trick fix the problem. I started getting P0421 after having an issue with engine misfire ( replaced ignition coil ) however by the time I put new coil in enough damage was done to the cat by the fuel that did not burn when and where it should have hence damaging the cat. I just hope now that I will pass the emission test next year.