I have a 2000 monty, endeavor model, and the engine light just came on. I self checked theerror code and it isP0421 which = Warm Up Catalyst Efficiency Below Threshold (Bank 1)
As of now the truck seems to be running fine, no changes in power and no strange sounds. Is this a matter that needs immediate attention or can it wait a few weeks?

Thanks -

Bob

 

If it's running fine, it may just be an 02 Sensor. Most that have had this warning need a new Catalytic converter.

 

If it is the Catalytic converter what am i looking at as far as ballpark cost for parts and labor?

 

I hear the cost is pretty high...but I don't have a figure. Here is some info on your code...maybe try the 02 sensor first as montero1 indicated?
http://www.obd-codes.com/trouble_cod...old-bank-1.php

 

Cat Converters aren't cheap, having someone else do it may cost $500 installed, just depends on who does it and what kind of part they use. Best thing to do is remove that sensor, and get it tested. Usually, they look really lite colored, like grayish when they're "done", though there is a way to test them, just don't know how.

 

OUt of the blue turned my Monty on today and the check enine light was gone - stayed off all day - Bad fuel maybe???Everything fine now -Thank for your input -

 

Hope it stays off for you.

 

That's an error for the Passenger side exhaust on the Montero Ltd. (I'm assuming the Endeavor is similar).

PCM (Powertrain control module) is monitoring voltages from the O2 sensor before the cat and from the O2 sensor after the cat and comparing their ratio. If the ratio exceeds .75 (a value of 1.0 would indicate exhaust is the same before and after the cat, obviously it should be much cleaner after the cat), this error code is set.

I would think that if one of the O2 sensors were bad, another code would have been set specifically for that sensor. Some possibilities :

1) Exhaust before the cat somehow got temporarily really clean (hole in the pipe?)
2) Exhaust after the cat somehow got temporarily really dirty (bad cat ?)

Was the vehicle sitting for an extended time, or was this a cold weather/ warm weather scenario?

 

This is timely since I just got hit with code 0431 which is the same thing on the driver's side.

Last year I had your problem - 0421 and ended up having to get a new cat and O2 sensor - $1,300 including labor! My light went on and off like yours for several months and then stayed on. If you have an OBD scanner you may see that there is a "Pending Error" or that the internal test cycleshave not completed even if the light is out.

Here in CA we can't pass a smog test with error codes showing so I was stuck. Mitsu dealer did a full diagnostic and said the cat was bad. The O2 sensor was seized in the port and had to be replaced as well.

Now it looks like I'm going to have to do the left side. I'm at 155K miles so It's probably time. This time I'm going to get a new sensor and try to replace it myself just in case that's the problem. No harm done if I then end up having to get a cat.

There us a Mitsu dealer in Rhode Island that sells the cats at a discount. They advertise on this forum.Still around $500 to $600. If you havean independent shop you trust you can bring them the part and hopefully save some $$.

Good luck (to us all)

Ron