YACT: Check engine light ODBII Code P0420

[d33pt]

I got my check engine light scanned at Autozone and it came out with code p0420: Catalyst system efficiency below threshold (Bank 1). What usually causes this code? I have a 99 2wd tacoma 2.4L auto with 110k miles. My guess would be the rear oxygen sensor because i really doubt the catalytic converter is dead after only four years. it also passed smog fine two weeks ago. Any help would be appreciated

 

[optoman]

Sounds like the oxygen sensor to me but I am no mechanic. Someone will come along and rectify the situation.

 

[JC]

edit: note to self: read thread first 😱

 

[Green Man]

99% of the time, OBDII is right about the cat.

If it was a lazy rear o2 sensor, it would trip an o2 code.

Sorry to be the bearer of bad news :frown:

 

[justint]

Originally posted by: SpookyFish
99% of the time, OBDII is right about the cat.

If it was a lazy rear o2 sensor, it would trip an o2 code.

Sorry to be the bearer of bad news :frown:

What could have caused the CAT to go bad? Isn't thier usually an underlying engine problem that causes this sort of thing? If he just replaces the cat, isn't it likely that the new one will just go bad as well if he doesn't fix whatever the problem was?

 

[d33pt]

Originally posted by: justint

Originally posted by: SpookyFish
99% of the time, OBDII is right about the cat.

If it was a lazy rear o2 sensor, it would trip an o2 code.

Sorry to be the bearer of bad news :frown:

What could have caused the CAT to go bad? Isn't thier usually an underlying engine problem that causes this sort of thing? If he just replaces the cat, isn't it likely that the new one will just go bad as well if he doesn't fix whatever the problem was?

That's a very good point too. How could I have passed smog with a bad cat though? They don't just go bad in one day...it's more of a gradual thing

 

[justint]

Originally posted by: d33pt

Originally posted by: justint

Originally posted by: SpookyFish
99% of the time, OBDII is right about the cat.

If it was a lazy rear o2 sensor, it would trip an o2 code.

Sorry to be the bearer of bad news :frown:

What could have caused the CAT to go bad? Isn't thier usually an underlying engine problem that causes this sort of thing? If he just replaces the cat, isn't it likely that the new one will just go bad as well if he doesn't fix whatever the problem was?

That's a very good point too. How could I have passed smog with a bad cat though? They don't just go bad in one day...it's more of a gradual thing

Have you gone under it and looked for impact damage? Hit it hard with the palm of your hand and see if you hear rattling? Have you kept your engine in tune (changed plugs etc.). Any chance you could have had some leaded gas put in the car by accident? I have also heard that fuel injector cleaner can sometimes damage a cat. Had a mechanice actually check the rear 02 sensor with a scan tool or alternately a digital multimeter? I have the same problem in my 98 Honda with 104k and I am debating whether to change the cat.

 

[d33pt]

I just got the truck last week. Funny you mention fuel injector cleaner, because I put in a bottle of Chevron Techron two gas tanks ago. That's BS if that messed up my cat. I will test that rear o2 sensor with a multimeter when I get a chance this weekend. You think it'll be bad to drive it around as is right now?

 

[JC]

Usually it's not the FI cleaner itself that hurts the cat, it's all the junk that it clears out, can clog the cat :| Sometimes kills the plugs, too.

I doubt that one bottle of Techron would loosen up that much junk, though.

 

[justint]

Originally posted by: d33pt
I just got the truck last week. Funny you mention fuel injector cleaner, because I put in a bottle of Chevron Techron two gas tanks ago. That's BS if that messed up my cat. I will test that rear o2 sensor with a multimeter when I get a chance this weekend. You think it'll be bad to drive it around as is right now?

Damn it. I had a funny feeling about the fuel injector cleaner. My cat started throwing that code within about 2k of putting in some STP fuel injector cleaner. I don't know why I did that, it isn't usually neccessary. Anyone have any more info on whether fuel injector cleaner can damage a cat??

 

[justint]

Originally posted by: d33pt
I just got the truck last week. Funny you mention fuel injector cleaner, because I put in a bottle of Chevron Techron two gas tanks ago. That's BS if that messed up my cat. I will test that rear o2 sensor with a multimeter when I get a chance this weekend. You think it'll be bad to drive it around as is right now?

P0420 should not put your car into Limp Home mode. Have you noticed your fuel mileage go down? As far as I know that code is just a warning. Have you tried resetting the engine computer and seing if the code comes back?

 

[d33pt]

light came on yesterday. I have not reset it yet. Autozone guy tried to do it with his scantool but it didn't reset. I think i have to pull the EFI fuse to reset it, but i haven't gotten the chance to do that yet. truck seems to run fine

 

[d33pt]

the o2 sensor costs $150!! that's ridiculous for the stupid sensor...damn i hate ODBII

 

[justint]

Originally posted by: d33pt
the o2 sensor costs $150!! that's ridiculous for the stupid sensor...damn i hate ODBII

That's actually not that bad for a sensor. Mine are around $175. At this point it looks like new cat for me. Either $150 aftermarket direct fit cat, or $550 OEM cat.