3.6 Pentastar P0420 + O2 Bank 1, Sensor 1 Codes

[muddyboots]

Engine light came on in wife's 2013 Grand Caravan (115k miles).
Cheapo scanner shows PO420 Powertrain:

and low voltage for O2 Bank 1, Sensor 1:

I'm making the assumption that the O2 sensor is the likely culprit and plan to change it out as a first step.
Is this a good assumption given these scan results, or should I do additional diagnostics?

Bank 1, Sensor 1 is the upstream sensor, before the cat way up under that by the firewall, right?

 

[JC1]

I would reset it first and see how soon it comes back. On my Sienna I'd get P0420 when it got really cold weather wise. After a reset it never came back for months at a time.

 

[clinebarger]

What's the O2 sensor fault code/DTC?? Catalyst Monitors will not run with O2 sensor DTC's for obvious reasons.

 

[2009Caraman]

Small chance of leak between sensor 1 and cat. or exhaust manifold.

 

[muddyboots]

What's the O2 sensor fault code/DTC?? Catalyst Monitors will not run with O2 sensor DTC's for obvious reasons.

There was no code for the O2 in the fault log, only the O2 "Not OK" error on the vehicle test results. (This is using the Torque android app.)

 

[SHOZ]

Monitor the pre and post cat O2s voltage. A good cat and O2s will show the pre cat one rapidly cycling the post cat maintaining a value above .600v, more likely near the high value you see on the pre cat O2 while warm and cruising.

Outside chance it is the O2s as they too are nearing the end.

 

[muddyboots]

Just graphed it with engine warm.
At idle it looks like this:

Bank 1 Sensor 1 is cycling between about 0.1 and 0.8, not dropping to zero.
Bank 1 Sensor 2 is an almost flatline up close to 0.8

Did a reset and cleared the codes. We'll see if they come up again.

 

[SHOZ]

Just graphed it with engine warm.
At idle it looks like this:

View attachment 52063
Bank 1 Sensor 1 is cycling between about 0.1 and 0.8, not dropping to zero.
Bank 1 Sensor 2 is an almost flatline up close to 0.8

Did a reset and cleared the codes. We'll see if they come up again.

That's good at idle, what does it do going down the road at a steady speed? The post O2 that is.

FWIW on my Hyundai's the test for this P0420 or other cat codes is done, after the car has warmed up to at least 150F then cooled down to under 150F with engine off. On restart as soon as it hits 150F again it will drive the engine lean twice and see how the second O2 responds. The second O2 should NOT go lean but stay above .500v while the Primary O2 is down low, ~.1 or .2v.

 

[Silver]

I would suspect the cat or post-cat sensor first. No?

 

[SHOZ]

The sensor is telling you the cat is bad. If the senor is bad they give separate codes. The post O2 if it has +100k miles may be slow and this will trip the code for the cat when the sensor is what is really bad. But in reality they both should probably be changed.

So change the sensor first.

I just went through this over the last three years with my Hyundai Accent. Found the manifold/cat for $125 on ebay last fall and two new OE sensors for $150. $3 for a 1" extension bung for the post cat O2.

 

[SHOZ]

It's also important to have a good primary O2. If it is slow to react more than likely the engine will be running lean yet within normal parameters (big LTFT#) and you are short changing the cat as far as 'storage' goes.

 

[w102dgg]

I had a 2011 Dodge Dakota that kept giving me this code and acted very much like what your describing, and it was due to a small crack after the pre catalytic converter O2 sensor. So I would look for leaks.

 

[rodinator1234]

I just had this same issue on my 2016 Jeep Wrangler. Changed both O2's and cat gasket, it does not have a manifold per say I noticed the cat had come apart. Had to replace the cat on that side, it was under warranty major emissions. I looked inside the cat when I had it off and it looked like it had broken one of the stainless band clamps that hold the two halves of the catalyst together. Vibration caused it idk, but it was destroying it's self. Had 58k miles on the Jeep. P0420 should be bank 1 sensor 2. Bank 1 sensor 1 is up stream of the cat that reads AFR/fuel trims, bank 1 sensor 2 reads catalyst efficiency.

 

[muddyboots]

Thanks for all the replies guys. Based on your comments, I will look for leaks, and plan to replace the O2 sensors first, then maybe the cat.
Taking a road trip in it this weekend, so I'll see if throws the code again, and will have the opportunity to watch it with the scanner.

 

[Turbo Actual]

I have the same code for Bank 1 Sensor 1 for my 2008 Nissan Pathfinder 4.0. Replaced multiple times and the cel light is still on after resetting it. Wires look fine. I’m hoping it’s not my cat. No power loss, no weird noises, just a higher idle than normal.

 

[muddyboots]

That's good at idle, what does it do going down the road at a steady speed? The post O2 that is.

FWIW on my Hyundai's the test for this P0420 or other cat codes is done, after the car has warmed up to at least 150F then cooled down to under 150F with engine off. On restart as soon as it hits 150F again it will drive the engine lean twice and see how the second O2 responds. The second O2 should NOT go lean but stay above .500v while the Primary O2 is down low, ~.1 or .2v.

Here's what it looks like with a warm engine, on the highway with cruise control set.
Getting voltage drops on the Bank 1 Sensor 2 (post cat).

 

[JTK]

Like said above, there's no exhaust manifolds on pentastars. The CCs bolt right to the cylinder heads. I haven't seen any catalyst inefficiency codes for pentastars yet. Can you hear any undue exhaust sounds?

 

[muddyboots]

Like said above, there's no exhaust manifolds on pentastars. The CCs bolt right to the cylinder heads. I haven't seen any catalyst inefficiency codes for pentastars yet. Can you hear any undue exhaust sounds?

Nope, no exhaust leak sounds as far as I can tell. Need to get it up on ramps so I can get under it and get a closer look. No codes on the road trip or since the reset.

 

[JTK]

Puzzling one given the low mileage and the vehicle isn't that old. Was it ever run with a misfire for any length of time?

The upstream and downstream sensors are basically built right into the cat. What you see is bolted directly to the cylinder head on pentastars.

 

[MattPersman]

We have seen many efficiency codes on pentastars. New cat with new o2s is the repair

seem em broken. Likely many are cracked as well that is not visual. Worse one was the entire element inside was missing