I have a 1998 3.0 CL with 171K miles, and I keep receiving the famous P0420 (catalyist efficiency below threshold (bank 1) engine code. I have recently replaced the the catalytic converter twice, and have also replaced both the primary and secondary O2 sensors with brand new OEM replacements. The muffler shop also confirmed that there are no leaks on the header, manifold, and the rest of the exhaust system. The engine light keeps coiming on after being reset just about every 70 miles with the same code. I have done lots of research on this topic and it seems to be a major issue for lots of cars besides Acura. What are my options at this time? The muffler shop that replaced my cat and O2 sensors told be that if I go to Acura, the first thing they will is replace the cat and both O2 sensors with genunie Acura parts (about $2k to do so). He said this will probably not clear the code. I heard that some car manufacurers have had to do an ECU reflash free of charge to correct this issue; however, I do not believe Acura has an ECU reflash fix for this. I would appreciate any and all options. Thanks.

 

So you changed all that stuff and its still throwing the code? Wouldnt hurt to call your dealership and see if they'll reflash the ECU for beans

 

i was told that a simple tune-up is what can be throwing that code.

 

I did a tune-up @ 110K with premium spark plugs.

 

with a gap of 61k, at least change your spark plugs.

 

what is the code for egr low flow.. i cant remember.. i thought that was the code for it. also asianspec is right, thats a long time between tune ups. let me do some research for the code..

 

ok the code is catlyst... my bad.. have you disconnected your battery yet? thatll clear all old and new codes.

 

To understand why you're ECU is presenting code P0420, you need a scanner that can monitor the O2 sensors, in particular the sensor after the catalytic converter.

When P0420 is set, the O2 sensor aft of the cat is sensing large and frequent changes in o2 content in the exhaust stream. The converter is supposed to either absorb or contribute O2 to cause the O2 level to stay relatively constant. This indicates proper functioning of the converter. When large, frequent O2 level changes persist for some time (70 miles or so in your case), the ECU interprets this as 'Inadequate Catalytic Converter Efficiency" or similar message.

If you scan the O2 sensor input (any OBD2 monitor w/ scanning function should do this), you are likely to see the rapidly fluctuating O2 levels behind the cat. If you get a nice smooth slowly changing O2 level, then you could have a bad ECU (very unlikely).

What can cause P0420? There are only a couple of things to my knowledge, 1) converter is fouled preventing the element cerium in the converter from storing adequate O2 to smooth the converter processing of hydrocarbons. 2) Excess O2 is entering the exhaust through a crack in the piping or exhaust manifold.

Even though you replaced the converter, did you use a 3-way catalytic converter equivalent to OEM? Some of the aftermarket converters are reported to not provide adequate O2 storage and will not fix your problem.

You may need an experienced Acura or Honda technician to solve this problem. It appears your previous mechanic has simply been throwing parts at the problem (at your expense) and hoping to get lucky. That works for him, but not to satisfactory from your POV. I would try a new mechanic.

good luck

 

get one of those oxygen sensor things for people with a test pipe.... i have one in my garage PM me if you want it

 

I did confirm that the converter installed is a 3-way cat. The entire system was checked for leaks and none were found. Acura already told me that if I bring the car to them they are automatically going to replace both O2 sensors and the cat with genuine Acura parts. About $2,300 - $2,500 with installation. Once they replace these parts then they will continue to further diagnose if the code comes back on. I am not willing to spend that kind of money to run off an engine light when the car runs fine. I talked to other Acura dealerships and it seems they are all the same in that they do not like to diagnose cars with non Acura parts.

 

Do you mean a MIL eliminator?

 

sure whatever you want to call it

 

you can also get a spark plug anti fowler, and screw it inplace and put the o2 sensor in it.. that will pull the o2 sensor out of the flow of the emissions. but that wont "fix" it. you might have to have someone hook up the ecu to a full system diagnosis. it will tell you exactly what the output and input of every sensor is on your car.. it will even tell you how many amps your dome light is pulling..

 

My ECU has been on for several months for the reasons mentioned above and still will not go out. Any other advice?

 

You might want to truly have the car checked out by an Acura specialist. Sounds like either your ECU is bad, or your o2 sensors are bad. Have you done anything since?

 

Are you willing to crawl under your car with a multimeter? I can post some troubleshooting steps if you are. Just warning, the procedures are not for the feint of heart, but also not difficult.
If not, like said above you need to take it to a Acura/Honda specialist (not necessarily the dealer). There are troubleshooting steps which will properly diagnose and identify the culprit. Run (don't walk) from any mechanic that will simply replace parts based on a CEL without troubleshooting.

 

As mentioned somewhere above, the Acura dealership insists on replacing the cat for $1,500K becuase the CEL is throwing the cat below threshold code bank1 code. The cat and both O2 sensors were replaced twice (using non Acura parts). The engine sounds better than ever, and my MPG is around 26. It has to be some kind of simple fluk with something; however, I am not about to give Acura several hundred $$$ to play experiment with parts on my car.

I would be more than glad to view your troubleshooting tips.

Thanks in advance.

 

I agree that another catalytic converter is not necessary.

I would suspect there is an exhaust leak that has not be detected (cracked exhaust manifold or gasket defect). That's about all that will cause P0420 w/ a good converter.

I would go to the mechanical fix alluded to by others. Below is a link to the fix on Subaru's which is same for any car. I used this on a Toyota Celica w/ a persistent P0420 and it's a permanent fix. It smooths the aft cat O2 sensor and eliminates the code.

P0420 Mechanical Fix

Regards

 

Before I consider this option, is it legal?

 

No, it is not legal.

good luck

 

guys, I know the thread is pretty old -- not sure since the time you guys posted to the present day what has happened but I had a P0420 code thrown at me today while driving home in my 05 RL...and there is a big flashing "Emission check" on my GPS system

anycase I did some research took it to an experience Honda Mechanic and he did a open flow test to check the emission on the 2nd O2 and confirmed that they Cat was okay. He then cleared the code. I am going to drive it to see if the code comes back. Ironically I just did a tuneup (air filter check, engine oil change, and drain and refill of the tranny)-- I checked everything and doubled checked...

So -- my question is has anyone been able to get the dealer to replace the Cat and everything has been swell since?

 

i think it was only covered by 97's only. mine is still there.

 

Can't find the link mentioned by TexasHonda for mechanical fix