Crap!!!

[masapell]

Ok, now that I got that out of my system. I NEED INSIGHT!! So, to all of the people who I highly admire out there because, unlike me, they know what they're talking about. I just want to be armed with information BEFORE I go to the dealership. My truck threw a P0420 this morning while casually going to work. Well, I called my friend at the dealership and he told me what it was and that he thought it was the catalytic converter. Now, my question is this: Is that always the culprit with this code, or can it be related to a bad
O2 sensor? If it is the cat, how hard is it going to be to find the engine culprit that caused it, and am I going to wish I had a bicycle after they tell what fixing it is going to involve? Any likely causes, scenerios, or possibilities would be greatly appreciated. Now let me go back to work!

Sincerely,
Matt

[j cAT]

the driver side cat is not properly working as it's oxygen storage capability has degraded below a calibrated threshold. this the definition of p0420... now going to the dealer to have this repaired you best be armed with a lot of cash as they will want to replace at least 1200.00 of parts.......my suggestion forget the o2 diagnostics IF your vehicle has over or close to 100,000 mi on the o2 sensors , as this is the expected life of these parts. just do it your self or bring to a non dealership repair shop and replace all 4 o2 sensors. if the problem returns just put the o2 sensors into the new cats. i would never replace a cat and use the old sensors as this could damage new cats quickly......especially if sensors are old..............if it is necessary to replace cats have diagnostics done after cat r/r to ensure that the engine emission management system is sound..........

[J-Ri]

More often than not the cause is a bad downstream O2 sensor. I have only seen this caused by a bad cat one time. If the cat is bad, it is because the engine is running too rich. Have your friend look at the fuel trim. +/-5% is considered good. +/-20% is acceptable in almost all cases.

[masapell]

I have not noticed any different driveability issues. The truck has 122,000k on it and seems to run like it normally does. As for the engine, I keep up with the maintenance on everything. Thanks for the information. I would hope that he would try and steer me in the direction of checking everything out before we go the real expensive route. If we have to, I am still not sure what could be the underlying cause.

Sincerely,
Matt

[j cAT]

I am still not sure what could be the underlying cause.

Sincerely,
Matt[/quote]

matt the cause is most likely the fact the the o2 sensors should have been replaced 22,000mi ago. hopefully your cat is still good........

[linis53081]

??? if you have code po420 and the cat is hot pre cat and cool post cat ould that mean the cats are still OK and its just the down stream 02 sensor's