PO420 code catalyst eff. below threshold What does this mean?
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Can only share the German reply to this code which should be the same as toyota's. @ my shop when the german cars have this code essentially the catalytic converter is not capable of cleaning things up well enough to satisfy the second o2 sensor located after the cat. 9 out of 10 times we wind up installing a new catalytic converter on the car and all is well Only drawback is big $ for a new cat . You can find them cheap on the net but you get what you pay for (cheap=less prescious metal content{platinum}, poor welds and bad fit) OE would be the best possible fit and quality. Good luck
With OBDII the system had to not only be designed to reduce emissions, it had to prove it is working. From 95+ on Land cruisers, there is a second oxygen sensor downstream from the catalytic converters. It needs to see the same sine wave type pattern as the upstream oxygen sensor, but greatly reduced. If the pattern is not changed, meaning no catalytic action inside the converters, the Malfunction Indicator Light will come on and a P0420 Diagnostic Trouble Code will set.
If the sensor shows very different readings from the front it will also set this code.
If the sensor shows no readings it can also set this code.
So...
the possible causes of a P0420 are:
Bad catalytic converters
Bad downstream oxygen sensor
A leak at the downstream sensor, or between it and the upstream. Often caused by loose bolts at the O2 sensor itself.
A bad heater circuit in the downstream sensor causing the sensor to not heat up and read properly or at all
to find out what it is you can replace all the parts for about $2500 or check it with a scan tool to watch the downstream sensor readings and see what it does.
If it changes at the same rate and amount as the upstream, the cats are bad
If it does not change at all, either the O2 is bad, or the heater in the O2 is bad, or you have a wiring problem. The first two being far more common.
If it goes lean and stays there, you have a leak.
If the sensor shows very different readings from the front it will also set this code.
If the sensor shows no readings it can also set this code.
So...
the possible causes of a P0420 are:
Bad catalytic converters
Bad downstream oxygen sensor
A leak at the downstream sensor, or between it and the upstream. Often caused by loose bolts at the O2 sensor itself.
A bad heater circuit in the downstream sensor causing the sensor to not heat up and read properly or at all
to find out what it is you can replace all the parts for about $2500 or check it with a scan tool to watch the downstream sensor readings and see what it does.
If it changes at the same rate and amount as the upstream, the cats are bad
If it does not change at all, either the O2 is bad, or the heater in the O2 is bad, or you have a wiring problem. The first two being far more common.
If it goes lean and stays there, you have a leak.
Not if it was from the cats back and its sealed up well before the second O2.
If the cats were replaced, then it could be a real possibility.
If the cats were replaced, then it could be a real possibility.
Had the same issue with mine, code 420, replaced cat with an aftermarket. Also installed the borla cat back exhaust. About a year later, the brackets on the borla broke, causing an exhaust leak where it bolts behind the cat. Code 420 again. I had borla replace the exhaust (under their million mile warranty) and also had the cat replaced again (it was still under warranty). Now I have a new cat, new exhaust. Couple of days later the CEL cam on again. DANG! This time it was for the 2nd O2 sensor, which I had already purchased to replace for PM. Replaced the O2 sensor, and I think this fixed it.
Here's what I would do if I were you:
1. Make sure dont have any exhaust leaks with the Borla, check you mounting brackets and make sure they arent broken, also check the second O2 sensor for leaks. This is easy to do, just have the engine running and feel for exhaust leaks around the connections. Mine was easy to feel.
2. Replace second O2 Sensor (downstream from the cat).
3. Wait.
4. If you throw the 420 code again, replace the other O2 sensor.
5. wait.
6. If you throw the 420 again, replace the cat.
The muffler guy that installed my cat said these things shouldnt go bad. I would replace the cat last if I had to go through this again.
hth,
randall
Here's what I would do if I were you:
1. Make sure dont have any exhaust leaks with the Borla, check you mounting brackets and make sure they arent broken, also check the second O2 sensor for leaks. This is easy to do, just have the engine running and feel for exhaust leaks around the connections. Mine was easy to feel.
2. Replace second O2 Sensor (downstream from the cat).
3. Wait.
4. If you throw the 420 code again, replace the other O2 sensor.
5. wait.
6. If you throw the 420 again, replace the cat.
The muffler guy that installed my cat said these things shouldnt go bad. I would replace the cat last if I had to go through this again.
hth,
randall
4WD Toyota Owner Magazine
SILVER Star
My 80 through one of these on a long trip recently.
I had it cleared, came back, had it cleared again.
That was 2000k miles ago and it has not come back again.
All I did was a WHOLE BUNCH OF NOTHING
I had it cleared, came back, had it cleared again.
That was 2000k miles ago and it has not come back again.
All I did was a WHOLE BUNCH OF NOTHING
powderpig
SILVER Star
I have had good luck with watching the OBDII graph reader and then seeing what is up. My experence is the the front O2 senser sometimes get lazy (lack of a better word) and does not respond to the gasses as quick as it need to. Where the rear O2 sensor is still good. Any how it is best to hook computer based reader that show graphs so you can watch both O2 at the same time to see which may be the culprit . my experence is that the cats are good for a lot of miles and do not need to be replaced(never had to while I have worked on 80's even with well over 200k miles). It usually has been the O2 if they are no leaks. later robbie
Is there any way of cleaning or servicing the cats? I ask because when i had my cats cut'n'turned i asked the muffler guy since they were off if he could clean them. He said there is nothing you can do.
Nope. Nothing you can do.
ryanjl
SILVER Star
Cats work by running the exhaust gasses over platinum to effect their chemical makeup by atracting nitrogen atoms out of NO2 and by oxydizing the CO molecules.
They go "bad" by having the platinum particles eventually carried off in the exhaust.
"Rebuilt" cats are basically opening them up and putting new platinum covered ceramic in place of the old.
They go "bad" by having the platinum particles eventually carried off in the exhaust.
"Rebuilt" cats are basically opening them up and putting new platinum covered ceramic in place of the old.
See, 80's got mad platinum yo 
.
.
powderpig
SILVER Star
Most stock cats are made with Platinum where alot of aftermarket cats are made with a cheaper material that does not last as long, pladium (my spelling sucks). Both work but it pays to know what you may be buying if buying aftermrket. Platinum last a considerbal long time, and is expencive to boot. later robbie
I am throwing the same code in my '95. Mine began when I got some water in the engine (enough to kill it and not be able to restart for an hour or so, big puddle in parking lot, long story...). I was thinking that this was caused by water getting down to the cats and shattering the ceramic, but this thread got me thinking it could be something else. I was going to send them in to get rebuilt, but now I am wondering if I shoud just replace the O2 sensors first and see if that clears the code. It wouldn't take the car down for as long while the cats are out. How much are new O2 sensors at the dealer?
alia176
SILVER Star
My P420 code comes up EVERY TIME I have an exhaust leak somewhere upstream of the second sensor. So far, the leaks were:
- at the location where the two downpipes come together. This "crotch" area had a slight crack/sepration that required minor welding
- minor leaks at the where the exhaust flanges meet up. New gasket solved that.
Good luck with your issue!
Ali
- at the location where the two downpipes come together. This "crotch" area had a slight crack/sepration that required minor welding
- minor leaks at the where the exhaust flanges meet up. New gasket solved that.
Good luck with your issue!
Ali
alia, same here. Had that code and found a leak where a new gasket fixed the problem. A while on down the road from that it popped back up. I replaced the O2 sensors and that has completely eliminated that code.
fj40fax said:
That's a good idea, especially if they're old. Lots of evidence around here that they slowly get "tired" and performance suffers.
Talk to cdan and find out:
https://forum.ih8mud.com/showpost.php?p=173756&postcount=1
Tell him you're a MUDer.
Curtis
Thanks, Curtis. I have a call in to Dan for a price quote, and will look/listen/feel for leaks when I get home today.
Thanks all,
Fax
Thanks all,
Fax
