P0430 With New Cats

So I've had a P0420 for years. At first it was intermittent, but then became a solid code a couple of years ago. In NJ we have to go through emissions inspection every 2 years. The truck is quite literally falling apart from rust, but mechanically it's fine. Runs good, 4WD works, so I figured I'd invest in the exhaust fix. I got a new set of cats from Eastern Catalytic and a Gibson exhaust system (which is quite nice and inexpensive). I also got 4 new O2 sensors.

With the new exhaust and O2 sensors installed, I unhooked the battery to recalibrate the fueling and cleared the codes. One by one the OBD-II monitors cleared and I was ready for emissions inspection. It passed, so I got 2 more years out of it so long as the body holds up.

At 125 miles since the exhaust fix the CEL came back on. It's a P0430 - cat on bank 2. No other codes. I cleared it, but it comes right back as soon as the cat OBD-II monitor runs. So...how do I diagnose? Eastern Catalytic won't process a warranty claim without a "trained mechanic" diagnosis which we all know consists of plugging it in and seeing a P0430 code. I'm not paying for a diagnosis.

I have a scanner that shows me expected and actual cat efficiency. I don't know if that's enough evidence for them. Not sure if swapping the new O2 sensors to bank 1 would make sense just to see if I get a 420 instead (indicating an O2 sensor problem rather than the cat itself).

It sucks because I was really enjoying the way the truck runs with the new parts - particularly the ability to remote-start it which I haven't been able to do in years.

Maybe one of the electrical gurus on the site will chime in soon but my guess would be to check the O2 sensor itself and consider replacing it or check for a proper connection with wires since you have commented about rust.
Also as a side thought why don't you consider fixing the rust while it is small areas and can be patched instead of just letting it act as a cancer to kill  your AV? Preventative maintenance can go a long way to help preserve a vehicle and keep it on the road for decades........It certainly would be cheaper then buying a new truck.

Vaeagleav said:

Maybe one of the electrical gurus on the site will chime in soon but my guess would be to check the O2 sensor itself and consider replacing it or check for a proper connection with wires since you have commented about rust.
Also as a side thought why don't you consider fixing the rust while it is small areas and can be patched instead of just letting it act as a cancer to kill  your AV? Preventative maintenance can go a long way to help preserve a vehicle and keep it on the road for decades........It certainly would be cheaper then buying a new truck.

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I'd love to save it but it deteriorated very quickly over the past couple of years. Every panel is rotted through - fenders, rockers, quarters, tailgate. There's a huge section of the frame rail missing behind the right front wheel. The front stabilizer bar isn't attached to anything anymore. The part of the frame where the rear lighting was grounded is gone - I had to rewire it and ground it at a part of the frame that still sort of exists. The mounting points for the rear ride height sensors are gone - they're flapping in the breeze. There is so much stuff banging around underneath that I expect something huge to drop off of it at any moment.

But, like I said, it still works. I use it to haul junk to the salvage yard and recycling center. I take it to work when the weather is bad. The interior has held up really nice and despite the things banging around underneath, it really does ride nice on the highway.

I don't know if it will last until the next emissions inspection in 2 years, but I really want to figure out what's going on. I paid for the parts and they should function properly no matter what condition the rest of the truck is in.

Here's factory info on a P0420 which is same thing, except it's for Bank 1 instead of Bank 2

https://blazerforum.com/forum/diagnostic-trouble-codes-dtcs-49/p0420-explained-19820/  You will have to join and be logged in to read it.

Here's the way the PCM checks out the catalytic converters:

A good catalytic converter will retain oxygen for a period of time.  A bad converter will not.  So PCM intentionally changes fuel mix as a test and sees how long it takes for the after converter sensors to respond to the change.  That is defined as cat efficiency.  If the delay is less than a prescribed amount, then the SES light is illuminated and the code P0420 or P0430 is set.  Also explains how it checks to make sure converter hasn't been removed or disabled.

It is possible that a misfire if present, or rich condition, or burning oil/coolant may have already ruined your new converter.

 

Thanks for the reply.

It's not burning oil, not running rich (no rich codes) and no misfire. It would be one thing if the P0420 came back - I'd be suspicious of something wrong on Bank 1. But it's never had a P0430 before so it can't be coincidence that it popped up with the new cats and O2 sensors. I'll have to plug in the scan tool to see what the sensors are reporting.

I guess I'm not quite understanding your logic.

IMHO watching the post cat sensors change in response to changed mixture input into the cat is a better way to test both the sensors and the cat converters.

Here I pulled the fitting out of the brake booster but held it close enough to the booster port that it would still idle (on a Blazer). In other words I created a big vacuum leak and watched all the O2 sensors go to full lean. This vehicle only had one post cat O2 sensor, but you can plot all 4 (Torque Pro was used in this case).  Then I plugged the fitting back in and took a screen capture of the resulting responses as it went to full rich (eventually the front sensors settle into the cycling shown in second screen capture attached) Note that at idle there was about a 2 second delay before the post-cat sensor responded to the richened fuel mix. From the code description as I understand it, this is the kind of testing the PCM actually does. If the time difference is too short, then it sets a P420. this could also be done with the logging function, but results in a table of values.

You should know that up front O2 sensors cycle rapidly back and forth below/above 0.45V when they are controlling the mix at 14 A/F ratio.  Any instantaneous record of their value is worthless unless they are pegged one way or another.  This is why O2 sensor voltage needs to be plotted to make any sense.  Post-cat O2 sensors should be steady (and same cycle cycling is indicative of a bad cat, but checking this way can trick you into thinking a cat converter is good if the post cat sensor is pegged either lean or rich).  IMHO the first way is better as it actually checks capacity of the converter to retain oxygen.

Note that both images are of a normally operating system with good cat converter and O2 sensors.

Good luck and best wishes for a successful repair.

First image is an example of a bad cat that wouldn't pass computer check.  Second image is inconclusive because post cat O2 sensor is pegged at 0.8V.  I don't have an image of the oxygen retention for a bad cat.

My logic is that I didn't have a P0430 failure in the past, so that should rule out any mechanical issue like a rich condition, burning oil or misfire. I mean it could be a coincidence that a mechanical issue fragged the new cat, but I don't believe in coincidences.

So that leaves the issue to being with one of the new parts on bank 2: upstream sensor, cat or downstream sensor.

My (inexpensive) scan tool doesn't have recording capabilities but it does graph real time sensor data. I'll try what you did to see how the sensors are reacting. Your explanation and screenshots were a big help. Thanks!

good luck.  Let us know what you find.

Is it possible to move the O2 sensors to different locations to see if the error follows a sensor?

I've never had to do this, so I'm just tossing out a random thought.

EXT4ME said:

Is it possible to move the O2 sensors to different locations to see if the error follows a sensor?

I've never had to do this, so I'm just tossing out a random thought.

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I agree, swap the sensors if possible. Easiest and cheapest method to diagnose the problem..

I had a misfire on number three cylinder and first I swapped plugs to number 6 cylinder with no change, then swapped wires with no change, then I swapped the coils and misfire followed. Installed a new coil and problem fixed to this day..

Good luck

Randy said:

I agree, swap the sensors if possible. Easiest and cheapest method to diagnose the problem..

I had a misfire on number three cylinder and first I swapped plugs to number 6 cylinder with no change, then swapped wires with no change, then I swapped the coils and misfire followed. Installed a new coil and problem fixed to this day..

Good luck

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Yeah I had the same experience with a coil pack.

The sensors aren't too hard to get at. I'm going to see what the scan tool says first, though. If it points to a lazy sensor then I know where to start.

turbojimmy said:

Yeah I had the same experience with a coil pack.

The sensors aren't too hard to get at. I'm going to see what the scan tool says first, though. If it points to a lazy sensor then I know where to start.

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FYI a lazy pre-cat sensor will have slower cycling of voltage up and down.  My examples were 80K mile sensors at idle.  They will cycle more rapidly as RPMs are increased to 2000 and held there.  AFAIK, no way to check post cat sensor laziness using the scanner.

Okay - so now I have a pending P0175 which is a rich condition on bank 2 in addition to the current P0430. So something might be going on with that bank, but I'm still hoping it's one of the new O2 sensors on that side. I never had a rich condition or cat efficiency issue on that side.

The upstream sensors are some cheap, off-brand sensors from Rock Auto. The downstreams are more expensive Densos which I've had great experience with. But, looking at the graphs it looks like maybe the downstream cat on bank 2 is dropping off once in a while? Or is it reacting to a potentially rich mixture or bad cat? I dunno. The upstream sensors seem to work mostly in unison while the downstream sensors are pretty far apart.

I'm going to swap the sensors one at a time starting with the upstreams to see what happens.

FYI downstream CAT sole purpose is to set CEL when CATS not working properly.

UPSTREAM sensors are the ones that do all the work of sending signals to ECM about how combustion went.

So if one upstream is crap it would contribute to all sorts of things on that side; this is why everyone is saying to swap left to right.

Especially now before they get CORRODED on from too many heat cycles ince brand new.

good Luck

ygmn said:

FYI downstream CAT sole purpose is to set CEL when CATS not working properly.

UPSTREAM sensors are the ones that do all the work of sending signals to ECM about how combustion went.

So if one upstream is crap it would contribute to all sorts of things on that side; this is why everyone is saying to swap left to right.

Especially now before they get CORRODED on from too many heat cycles ince brand new.

good Luck

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Thanks - I'm going to swap the upstream sensors. Just need to find the time to do it...probably over the weekend.

turbojimmy said:

Okay - so now I have a pending P0175 which is a rich condition on bank 2 in addition to the current P0430. So something might be going on with that bank, but I'm still hoping it's one of the new O2 sensors on that side. I never had a rich condition or cat efficiency issue on that side.

The upstream sensors are some cheap, off-brand sensors from Rock Auto. The downstreams are more expensive Densos which I've had great experience with. But, looking at the graphs it looks like maybe the downstream cat on bank 2 is dropping off once in a while? Or is it reacting to a potentially rich mixture or bad cat? I dunno. The upstream sensors seem to work mostly in unison while the downstream sensors are pretty far apart.

I'm going to swap the sensors one at a time starting with the upstreams to see what happens.

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Based on your screen shots it is often staying above 0.45v on Bank 2.  Check your LTFT for both bank 1 and bank 2.  Also, a screen shot at 2000 rpm steady would be useful.

2004Slickside said:

Based on your screen shots it is often staying above 0.45v on Bank 2.  Check your LTFT for both bank 1 and bank 2.  Also, a screen shot at 2000 rpm steady would be useful.

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I'm going to swap the upstream sensors first. I feel like I'd just be chasing ghosts by doing more analysis. There were no bank 2 issues at all - ever - until I installed the new exhaust system and O2 sensors.

Ok then.  I tried.  Best wishes.

Just a thought many cars/ trucks have issues when you change the exhaust because a lack of back pressure on the exhaust. You may want to try cleaning the Maf sensor and running some good fuel system cleaner though it. If you can a scanner  and watch the duty cycle of the injectors. Usually this happens when folks add headers especially long tube headers

MS03 2500 said:

Just a thought many cars/ trucks have issues when you change the exhaust because a lack of back pressure on the exhaust. You may want to try cleaning the Maf sensor and running some good fuel system cleaner though it. If you can a scanner  and watch the duty cycle of the injectors. Usually this happens when folks add headers especially long tube headers

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My son was having that issue with his GTP. We put headers and 3" exhaust on it around Christmas time. He was getting a P0420. We cleaned the MAF and unhooked the battery to force fuel recalibration. The P0420 hasn't come back yet (knock on wood).

So I swapped upstream sensors on the Avy. The driver's side is a total Female Dog to get plugged back in but I finally got it hooked back up. It looks like the issue followed over to bank one now. The cat monitor didn't run yet, but the same low voltage on the downstream sensor is now on bank one where it was previously bank 2.

Looks like you may have found the problem, then.

EXT4ME said:

Looks like you may have found the problem, then.

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Yeah I should have googled the Ultra-Power sensors for reviews before I bought them. They're terrible, evidently. They're $19 while the Denso's are $40. There's a reason for that. I'm going to suck it up and buy a pair of upstream Denso sensors. I ran a Denso sensor in my GN - race fuel, alcohol and extreme heat didn't kill it.

Good move.

So the cat monitor finally ran today and the P0430 came back immediately. So it's not the upstream sensors. Good news is I can get my $80 back for the Densos I bought.

Long term fuel trim looks okay - Bank1 and Bank2 aren't too far apart. It's pulling slightly more fuel on Bank2 but it's not like it's pegged and running rich.

So once it cools off I'm going to swap the downstream sensors between banks. They're much easier to get at, too.