Check Engine Light - Code P0420

[mb12345]

I have a '97 Lexus ES300 (105K miles) and got a check engine light 2 days ago. I got it checked and it comes up with a P0420 code. The code description says "Catalyst System Efficiency Below Threshold (Bank 1)".

As I understand, it could be due to a defective catalytic converter, damaged O2 ensors, contamination of converter due to incorrect sealant, fuel, or fuel additive.

I had 2 repairs/services done on my car in the past 6 weeks:

1) I had replaced the flex pipe and the catalytic converter about 6 weeks ago. The flex pipe was leaking and the exhaust was making a lot of noise. My mechanic advised that I also replace the cat. I got the aftermarket (generic) flex pipe and cat.

2) I had a service done a week ago. I got the transmission liquid flushed, radiator coolant flushed and fuel injection service done.

My guess is I am getting this code due to something gone wrong in either of the above 2 repairs/services. The most obvious cause would seem to be the first one, but I don't know if I can rule out the second one as that was the most recent one ( a week ago).

I would appreciate if someone could help me with this. Could the second service cause P0420 to be set? Or is it possible that I just got a bad converter in repair 1? If yes, then would it take upto 6 weeks for the code to be set?

Any additional advice or suggestions would be appreciated.

Thanks,

-MB

[camlex]

Your O2 sensor after cat. needs to replace also, if you look your cat., if you will puple strips that is indication of burt(Damage) cat.

i was there, my mechanic replace cat. under warrenty.

FYI.

O2 sensor after cat. wiring conector is under driver seat.

Hope that helps.

[yeskay]

Your O2 sensor after cat. needs to replace also, if you look your cat., if you will puple strips that is indication of burt(Damage) cat.

i was there, my mechanic replace cat. under warrenty.

FYI.

O2 sensor after cat. wiring conector is under driver seat.

Hope that helps.

Camlex:

in the other post you mentioned that you have to strip the vacuum line in one end. is that not the fix.

[camlex]

I thought so, but I was wrong.

[mb12345]

Thanks everyone for your insights, suggestions and advice.

I just wanted to post an update that my check engine light went away

this evening. I did not do anything yet. I went to work in the morning

and the light was on. When returning from work, I turned on the car

and it was gone. I have made a couple of short trips since then

and the light has not come back on. Based on this occurence, I would

again have to lean on the experts here to understand what this means,

and if it may have temporarily disappeared and could return again.

Another problem that I didn't bring up earlier, as I did not want to

divert attention from the CEL problem, was that my fuel mileage had

dropped since I had replaced the catalytic converter. Previously I

would get about 24mpg and after replacing the converter I am getting

around 20mpg. I noticed the drop in mileage after replacing the cat

and before the fuel injection service. I have to ask this dumb

question, but can the replacement of the cat. converter cause a drop

in the mileage too (i.e. if I have a bad cat.) ?

Thanks everyone for your help.

[lenore]

I have heard, but cannot confirm that some aftermarket cats are really inferior. Maybe there is too much backpressure or the cat itself doesnt breathe as well. The Maf could also be dirty. there is a cleaning procedure for those.

[mb12345]

My check engine light came back on. So in a matter of the past 2

weeks, the light came on, then went off and came back on.

I paid $250 for the flex pipe + converter, and yes, this is most likely a universal converter and not a direct fit as the mechanic had to weld it in.

I did take my car back to the mechanic (the light was off that time),

he inspected and did not find any leaks. He still welded it again just

to close any minor leaks that may be present. The light came back on a

couple of days later, so don't think the second round of welding did

any good. Other than this, he does not see anything wrong in 'his'

converter.

What are my options at this point? Do I have to now go and buy a new

OEM converter?

[cp6689]

My check engine light came back on. So in a matter of the past 2

weeks, the light came on, then went off and came back on.

I paid $250 for the flex pipe + converter, and yes, this is most likely a universal converter and not a direct fit as the mechanic had to weld it in.

I did take my car back to the mechanic (the light was off that time),

he inspected and did not find any leaks. He still welded it again just

to close any minor leaks that may be present. The light came back on a

couple of days later, so don't think the second round of welding did

any good. Other than this, he does not see anything wrong in 'his'

converter.

What are my options at this point? Do I have to now go and buy a new

OEM converter?

mb12345,

Did you resolve your issue? I have a '01 ES and its gas mileage drops poorly in this winter too. I am curious about your current progress. Thanks in advance if you can share.

[camlex]

Please update...........

[in_slow]

I have a '97 Lexus ES300 (105K miles) and got a check engine light 2 days ago. I got it checked and it comes up with a P0420 code. The code description says "Catalyst System Efficiency Below Threshold (Bank 1)".

As I understand, it could be due to a defective catalytic converter, damaged O2 ensors, contamination of converter due to incorrect sealant, fuel, or fuel additive.

I had 2 repairs/services done on my car in the past 6 weeks:

1) I had replaced the flex pipe and the catalytic converter about 6 weeks ago. The flex pipe was leaking and the exhaust was making a lot of noise. My mechanic advised that I also replace the cat. I got the aftermarket (generic) flex pipe and cat.

2) I had a service done a week ago. I got the transmission liquid flushed, radiator coolant flushed and fuel injection service done.

My guess is I am getting this code due to something gone wrong in either of the above 2 repairs/services. The most obvious cause would seem to be the first one, but I don't know if I can rule out the second one as that was the most recent one ( a week ago).

I would appreciate if someone could help me with this. Could the second service cause P0420 to be set? Or is it possible that I just got a bad converter in repair 1? If yes, then would it take upto 6 weeks for the code to be set?

Any additional advice or suggestions would be appreciated.

Thanks,

-MB

[busoptr]

My check engine light came back on. So in a matter of the past 2

weeks, the light came on, then went off and came back on.

I paid $250 for the flex pipe + converter, and yes, this is most likely a universal converter and not a direct fit as the mechanic had to weld it in.

I did take my car back to the mechanic (the light was off that time),

he inspected and did not find any leaks. He still welded it again just

to close any minor leaks that may be present. The light came back on a

couple of days later, so don't think the second round of welding did

any good. Other than this, he does not see anything wrong in 'his'

converter.

What are my options at this point? Do I have to now go and buy a new

OEM converter?

mb12345,

Have you even checked the connectors from the 02 sensors at all? It could be just loose from that recent work on your catalytic converter.

Did you resolve your issue? I have a '01 ES and its gas mileage drops poorly in this winter too. I am curious about your current progress. Thanks in advance if you can share.