P420 and 421

J

jason2000ls

Active LVC Member
Joined
Apr 30, 2012
Messages
57
Reaction score
0
Location
manitoba
Ok just got my codes read and I'm showing p420 and 421. Passenger side.. I have no vacuum leaks or exhaust leaks and its not the cats (I've had them hollowed out for quite some time with o2 cheaters with no issues what so ever. So now question is would this be my upstream or downstream o2 sensor ?? I assume if the anti foulers were ineffective I'd also have a p430 or 431? And no misfire codes whatsoever. Help is always greatly appreciated ...
 
Gas mileage has decreased slightly. Raw un burnt fuel smell noted (worse then when cats were originally gutted). Upstream bank 1 o2 ? Lastly I'm not sure if this apples to the ls . But could I use my downstream sensor on drivers side and swap it with the upstream of the passenger side to see if fuel mileage and performance improves ? The car runs great but I can feel something Is off the slightest bit . Do the downstream sensors only illuminate cel with out affecting performance
 
i assume you mean p0420 and p0421?

if so,
Catalyst System Efficiency Below Threshold (Bank 1).
since you have no cats, that is absolutely your problem.

no why is it only on one bank? i dunno. just lucky i guess.

the raw unburnt fuel smell is probably what killed your cats to begin with.
and is causing your decreased fuel mileage as well.
ie, you have at least one bad ignition coil. probably more.
 
Bad coil(s).
Replace all COPs and spark plugs.
 
Coils are 3 weeks old as well as plugs and valve cover gaskets . I highly doubt it's a fluke one side works and the other doesn't . Any other guesses? Not to mention it was fine after coils and plugs were done. Wouldn't I get a misfire code or blinking check engine light ?? I've checked every coil individually and there all working ..
 
I'm absolutely sure this isnt a coil problem. It feels like o2 sensor or egr issue. Now if it were egr related would it not cause both 0420 and p0430?? The fact that its only one side and it was running perfect for 2000k after cats were gutted leads me to believe it was something else . The p0420 code would show up within 50 miles when the cats were bad. I guess ill just switch o2 sensors and see if it thows a p0430 and p0431 just to be sure
 
Yes, it might not be coils, but it is always good to consider the more common problems first.
What brand of coils did you use?
The thing that is pointing me in that direction is the gasoline smell.
Marginal coils on the LS very rarely give a misfire code or flashing light.
 
Might be a good idea to go back and check to be sure all the COP(coils) connectors clicked in fully and correctly.
Smell of fuel past CATS is always unburned compression ... a clear sign of a no-fire on a cylinder somewhere.
 
If the engines tricked into throwing more fuel than necessary because its not getting the right exhaust readings from the cat that pops up... had to replace my sensors recently because of that.. and thank god it wasn't the cats
 
Switch the O2 sensors from right to left and see if the codes change. If they do the sensors are suspect, other wise it might be a CAT problem.
 
You must log in or register to reply here.

Members online

No members online now.
Total: 126 (members: 0, guests: 126)
Back
Top