First P0420 - next steps to check...

2008 4.0L here with 313k miles. I went to start my truck and the MIL came on. It was not on prior to shutting it off. I pulled the codes on the way home and saw P0420. I reset the codes on the way home to see if it comes back.

The truck seems to be running fine. I actually just got back from 3500 mile road trip about 2 weeks ago. No lights whatsoever and zero oil consumed. Also, the secondary cats are relatively new and were installed by the dealer about 3 years due to theft while driving home from a road trip.

What stinks is that my emissions test is due in a month. Talk about bad timing. Assuming it comes back on, is there anything I can check with my basic OBDII scanner and the OBD Fusion app to diagnose further?

Thoughts? Appreciate the help as always.

 

Depending on how thorough your emissions testing is in your state, you can Band-Aid using the sparkplug non fouler trick on the cheap but if there's an issue with your cats then it'll likely fail a sniffer test. If your sensors are original then it may just be time to replace them. I haven't heard many people having much luck with any type of cataclean. Another thing you can check would be for any leaks around where the header connects to the y-pipe and where the y-pipe connects to the tail pipe. It's not much to go on but it's a start. If I were you, I'd check for leaks first. If you don't find any, then I'd replace the sensors. You'll need to drive it for a few drive cycles to get the code to clear on its own. If the code doesn't clear on its own after a few drive cycles and you don't want to have your cats checked/replaced again, then I'd do the non-fouler trick and be done with it. Hope that helps.

-J

 

My state does check for codes including the catalyst monitor. My plan is get it in the ready state today and hopefully it will stay off long enough to take the test. Then I can at least deal with it later. I don't even want to think about replacing an exhaust manifold. The good news, if any, is that the exhaust manifolds have been off last year and all the mounting hardware has been replaced so no issues with rust to deal with.

My first step,, assuming the light comes back on, is to check for leaks. I doubt I will find any since the exhaust manifold gaskets were replaced including the ones between the upper and lower cats. Everything I read so far indicates that an O2 sensor is rarely the case in a modern two sensor per bank system. If I wrong, please let me know.

Some times I wonder if my 313k mile 2008 with 3 owners previously has had enough...

Btw, P0420 is bank 1, so I assume that is the passenger side where cylinder #1 is?

 

After you fix your problem, you'll need to complete a drive cycle. See this link on how to accomplish it. Just clearing the code will not necessarily remove the code as it will merely mask it into a "pending" status. You'll need to complete the drive cycle in order to clear it. My guess is that it prevents people from just clearing codes prior to a systems check and getting that green light. The non-foulers more than likely will clear the code but any observant technician will see them and flag it. Check for leaks first.

-J

 

I recently had this pop up. Same side for me, too. Swapped the O2 sensors from side to side to rule that out. Sensors were fine (unfortunately). Ended up getting all new manifolds/cats.

If you do swap sensors to rule that out, the Passenger side cable is shorter than the Driver side, so you'll need to remove the bracket to give enough slack to test, but it can be done. I just put a longer bolt in the bracket and that worked well for me.

My truck only had 129K on it, so if you made it to 300k+ on original cats, that's pretty sweet!

 

FYI..... another good thread on this exact issue. https://www.tacomaworld.com/threads/0430-and-0420-code-hell-d-fixed.406596/#post-11405772

 

Thanks everyone for the responses. I just got back from my emissions test and passed. I had my OBD2 scanner plugged in on my drive there so I could see when all monitors were ready for testing. No codes were set so I passed. Illinois doesn't do a visual they just plug into the OBD2 port and check the monitors and whether the MIL is on.

I'll take a look at the thread referenced above for more information. After doing the head gaskets and fuel sending unit over the past year, I'm kind of burned out on taking on more wrenching at this point. If the code does come back, I will look at the leaks first when I get a chance. I'm doubtful that there are any but I would need to check that nonetheless.