For the last year and a half I have had constant 420/430 CELs with brand new lower O2 sensors and no other problems. Although the manufacturer of my Hi-Flo Cats claims they've never had a problem, I have heard that sometimes they "can" be the culprit. I didn't have enough room for the double spark plug extender fix, but then I ran across this video by an Electrical Engineer.

https://www.bing.com/videos/search?q...2D25B9362555CF

I used one 1 Mohm, 1/4 watt resistor and a 4.7 uf capacitor per side (see photos 1 & 2). The Engineer discusses possible ranges for these. Get them from Radio Shack - Cheap! I also use a torch to solder - much faster, but watch where you point that thing! (Don't ask - lol)

Two weeks ago I finally got up the courage to do the surgery on the sensor wires to the RH sensor. It was much easier to just unplug the connector and let it dangle from the car than to remove the sensor (as in the video). For the next week, the only CELs I got were for the LH - great! So last week I did the other one as well, and 1500 miles later, my dashboard has finally been CEL FREE!!! As you can see from my pictures, I did the mod at the "connector" end; the video shows the mod at the "sensor" end. The orientation of the capacitor is important, so by all means,watch the video, but match my photos exactly!

1. You'll only be working with the blue and white wires, so get the black ones out of the way (photo 3).
2. I used a clamp to hold the black plastic sheathing up and out of the way. Don't cut any of it off.
3. Cut a section out of the blue wire, so that when the resistor is installed both the blue and white wires are still the same length.
4. Place some shrink wrap way up onto both wire ends so that after the resistor and upstream end of the capacitor are soldered-in you can cover it all up (photos 3 & 4).
5. Clear off some insulation from the white wire.
NOTE: The capacitor arrow must go from the blue wire to the white wire and it must be soldered in on the "connector" end of the resistor.
6. Design the installation so that the capacitor and the resistor are not side-by-side.
7. Solder the downstream end of the capacitor to the white wire. I made sure this exposed area wasn't in a position to touch the other end of the capacitor wire, but I put a couple of wraps of electrical tape on it anyway (photo 5).
8. Now you can take off the clamp and pull the black sheathing back over the whole installation. It looks perfectly normal - cool.

Reconnect the connectors above the transmission and enjoy CEL-free driving! I made sure to route the wires away from the Cats to protect the components from excessive heat. This has worked so well, I am beside myself! (spoken with best 7-Eleven accent - lol)

Somebody please put this in the Maintenance Fixes section of the forum.

Good luck guys