P0421 Odb code

[themodefanatic]

HELP. getting P0421 code. Relaced both O2 sensors, all spark plugs, all coils, egr valve and last but most expensive both catalytic converters (one attached to exhaust manifold & one underneath car. ) still getting code. HHHHEEEELLLLLPPPPP.

 

[winston3x]

check for vacum leaks?

 

[NocturnalSpeed]

Check Engine Light Codes

Best I can do... P0421 ---> Warm Up Catalyst Efficiency Below Threshold (Bank 1)

 

[RABID_MP5]

how did it RUN, both before and after the changes? I'm assuming OK, if it's just a catalyst efficiency detection issue.

If so, do you still have the old O2 sensors? I'd be trying different combinations of them in the primary and secondary positions. The ECU wants to see a difference between the 2 O2 sensor outputs - this indicates the first cat is oxydizing some unburnt fuel. (guys with headers and no first cat often play with the sensor positions to achieve this difference between sensors. Was that a p0420 catalyst efficiency or P0421 warm up catalystefficiency error we get on the headers??? I'm thinking the first cat is the "warm-up catalyst" put real close to the engine so it heats up and works quickly)

Since higher O2 concentration gives a higher voltage, and new sensors tend to be slightly more efficient, I'd try an old sensor in the second (bottom) position. How long does it take for the light to come on? Might take a lot of time to solve it that way without reading the ECU errors pending.

 

[themodefanatic]

All vacuum lines have been changed also. Included fresh air intake hose which was practically disintegrated. Somebody told me to check the intake manifold gasket. Runs great before and after the O2 sensors change. Still had old O2 sensors will try to use old ones in some combination to see if that's the problem. Car runs great small drop in idle every so often now. Which leads me to vacuum leak (i.e. Intake manifold gasket , vacuum leak. )

 

[RABID_MP5]

yeah I'd pursue the cause of the idle fluctuation first. If it's a new first cat, messing with the O2 sensors shouldn't make any difference really - they might if that cat was about shot.

Do they test emissions where you are? If not, remember if you can get it running great you can tape over the light or pull the bulb. My bulb is burned out because I have a constant error from me removing my EGR valve. The cat error per se is only an emissions issue. But it's looking like that error may be being triggered by other faults.

 

[slavrenz]

All vacuum lines have been changed also. Included fresh air intake hose which was practically disintegrated. Somebody told me to check the intake manifold gasket. Runs great before and after the O2 sensors change. Still had old O2 sensors will try to use old ones in some combination to see if that's the problem. Car runs great small drop in idle every so often now. Which leads me to vacuum leak (i.e. Intake manifold gasket , vacuum leak. )

It's not vacuum leaks you need to be looking for - it's exhaust leaks. There are only a few things that can cause a P0421 code to set - a bad front O2 sensor, a bad cat, or an exhaust leak. You've replaced all of the parts, so the only thing left is an exhaust leak. My guess would be between your exhaust manifold and the front cat.

Seriously though, throwing parts at the problem is about the worst way to solve an issue with your car (and when you're dealing with cats, sickeningly expensive). If you don't have the tools to diagnose this properly, you need to take it to someone that does. If every other possible cause gets ruled out, the only other explanation is a bad computer.

 

[slavrenz]

yeah I'd pursue the cause of the idle fluctuation first. If it's a new first cat, messing with the O2 sensors shouldn't make any difference really - they might if that cat was about shot.

Do they test emissions where you are? If not, remember if you can get it running great you can tape over the light or pull the bulb. My bulb is burned out because I have a constant error from me removing my EGR valve. The cat error per se is only an emissions issue. But it's looking like that error may be being triggered by other faults.

This is terrible advice - you'd have no way of knowing if another issue with your car ever arises. And if they do test your emissions and they find out that you did this, you're looking at mucho $$$ in fines.

 

[slavrenz]

how did it RUN, both before and after the changes? I'm assuming OK, if it's just a catalyst efficiency detection issue.

If so, do you still have the old O2 sensors? I'd be trying different combinations of them in the primary and secondary positions. The ECU wants to see a difference between the 2 O2 sensor outputs - this indicates the first cat is oxydizing some unburnt fuel. (guys with headers and no first cat often play with the sensor positions to achieve this difference between sensors. Was that a p0420 catalyst efficiency or P0421 warm up catalystefficiency error we get on the headers??? I'm thinking the first cat is the "warm-up catalyst" put real close to the engine so it heats up and works quickly)

Since higher O2 concentration gives a higher voltage, and new sensors tend to be slightly more efficient, I'd try an old sensor in the second (bottom) position. How long does it take for the light to come on? Might take a lot of time to solve it that way without reading the ECU errors pending.

1. We only get a P0421 code on our cars for the warmup cat, since there's no O2 sensor monitoring the rear cat.

2. Yes, it is called a warmup cat because it is close to the exhaust manifold, and therefore will "light off" much faster due to the extra heat from the engine. Catalytic converters need to reach a minimum temperature to work effectively (something like 500 or 600 degrees), and this is the best solution for reducing your emissions quickly at startup (which is when you get your worst emissions anyways due to the cold engine).

3. I severely doubt that going back to the old rear O2 sensor would fix things. If so, then the cat was getting ready to fail anyways, and was just barely on the edge in terms of the maximum allowed switching activity for the rear O2 sensor.

 

[themodefanatic]

Finally gave up. Took to dealer. Said wrong plugs were burning to hot fried pre-cat. Makes sense. Had to find right plugs. Pre-cat on order. Luckily I have a friend with business license who can get it at cost. Also tried to tell me second cat is bad ( it's three weeks old) possible but highly unlikely. I hate this car has been nothing but trouble since I bought it. Sad.