DTC P0420

[jlocster]

My truck just threw a CEL yesterday with p0420. It's supposed to refer to a bad catalytic converter. Has anyone here dealt with this code before on a Montero with California emissions? Coincidentally, I just installed new upstream o2 sensors last week.

 

[MonteroLTD]

9 times out of 10, it's the catalytic converter that needs replacement.

 

[Toasty]

Yup, and since it's a Cal truck it's more than likely the one up near the manifold. I've seen two of those this year, wonder if we could convert to Fed? anyone know if you could go to a single cat with 4 o2 sensors?

 

[SirFrancisDrake]

Coincidences are funny, my truck just threw a p0174 so I just ordered some new o2 sensors. I am curious about the cat as well... there is more than 1?

 

[Toasty]

CAL emissions has 2 and FED has 1, the other thing that looks like a catalytic converter is a resonator. If you have 2 cats they will be very close to the manifolds, one under the bellhousing and the other to the right of and tucked up there.

 

[mapper]

P0420 means your downstream O2 sensor is reading catalytic converter functioning below efficiency. Yes, it could be your cat but also could be a faulty O2 sensor. If your truck has been burning oil, however, due to valve stem seals...it can be real tough on a cat.

 

[twocommas]

P0420 means your downstream O2 sensor is reading catalytic converter functioning below efficiency. Yes, it could be your cat but also could be a faulty O2 sensor. If your truck has been burning oil, however, due to valve stem seals...it can be real tough on a cat.

Mine has been burning oil likely due to valve stem seals and I had the same code pop up about 6 months ago. Had it reset once, twice, and it never came up again. Maybe try that first before ordering a new cat or o2 sensors?

 

[MonteroLTD]

Sensor operation can be checked with a scan tool. Typically, a failed sensor will trigger a sensor fault code. So in my professional opinion, repair everything that could cause damage to your catalytic convertor (Misfire, oil consumption, etc.). Once that's been taken care of, you may replace the catalytic convertor.

 

[SlimPickins]

Anyone find a fix for this code/CA emissions issue?

 

[plh]

perhaps try a pair of spark plug non-fowlers on your O2 sensors

 

[SlimPickins]

Never heard of this so I had to look it up. Just brilliant, thanks plh. I'll give it a go and report back.

 

[SlimPickins]

My understanding is that I only need to do the post cat sensors..

 

[plh]

https://www.expeditionportal.com/forum/threads/gen-3-cats-downpipes.160630/

 

[SlimPickins]

So I got the non-foulers rigged up. The only difficult part was getting the old O2 sensor out. I rented O2 sensor sockets from O'Reilly and the non-foulers I purchased from them were like butter to drill out. I put a dab of anti-seize, put put everything together and unhooked the battery for a few minutes to get rid of the CEL. Now I just need to put on the required miles for 'readiness' and hope the CEL doesn't come back on. Then, off to emissions. Eventually I'll have to sort out the problem but a decent band aid for now. Thanks all for the input. Will follow up..

 

[Salonika]

Your emissions inspections don’t include a visual inspection by the technician? They won’t notice this thing?