Another P0430 / P0420 Thread - BlueDriver results

Well let’s see here... ‘05 with 164k miles, replaced hg at 142k miles about 1 1/2yrs ago due to cylinder 4 misfire code.

Since the leak, I’ve been fighting the P0420 and P0430 codes. Generally intermittent, and I’ve mostly been ignoring and just resetting the codes if and when they come up. Interesting to note though, the code or codes come up more often when I need to take side roads/steep roads that in general work the truck a bit more than normal. P0430 Bank 2 comes up more often (the side opposite my hg leak) than Bank 1, but both occasionally show up. My basic thinking is that the cats got damaged by coolant, which actually only explains one side but yeah anyway, I also know the code could be set off by faulty O2 sensors or A/F Sensors so I’m looking to confirm whether that might be my problem, not the cats.

So in trying to confirm O2 sensors, I bought some fancy phone scanner, bluedriver. The results are a bit confusing to me, I am concerned bluedriver isn’t picking up the quick oscillations of the O2 sensors, but also a bit confused about the air fuel ratio sensor versus O2 sensor. Sensor 1, The AF sensors, hang pretty steady around 3 1/2 V. Sensor 2 (the first O2 sensor, but after the first cat), jumps up-and-down as you would expect a sensor 1 O2 sensor to do, but seemingly inconsistently overall, but they do react when I hit the accelerator. I will attach some snapshots of the results. Anyone who can help me interpret this data, please speak up! I can do more tests and post more results as needed.

Also I should mention, I have new spark plugs, recently cleaned mass airflow sensor, change air filter, heads and cylinders are sparkly clean, I have run fuel system cleaner, basically anything you can think of like PCV valve cleaning intake and throttlebody cleaning, all done. Only thing I haven’t done regular maintenance-wise that I can think of is check fuel pump/fuel filter/fuel regulator.

 

I am not trying to hijack your thread, but I think we both need the same information to solve our problem.

It is nice to have all of the data, but it is difficult to interpret without knowing was good data looks like. I have similar issues with my 2005, with 109,000 miles. Just got it, so I am unsure of the history. I just got a phone scanner also... ODB Fusion for my old iPhone. Right now I have only code P0420. So bank one is affected.

I have graphs of similar data for my issue although they are different format. I think the O2 voltage graph on yours shows something wrong. While both banks show the #1 sensor very similar, the Bank 2 Sensor 2 graph is vastly different from the B1S2 graph. With B1S2 only showing variation at about 32 and 55 seconds.

Here are some graphs I got to compare. These are the O2 voltages from start up to about 4:30


Then I captured the cat temps. From start up to 6 minutes in.



I am not sure if mine are right are not. It seems that the O2 voltages are reacting in similar manner between both banks, although the B1S1 sensor seems more slow to react than B2S1.

The Cat Temps are troubling to me as I thought the exit temps would be higher than the exit temp, however both banks appear to be so close they may as well be the same.

I would love to see some scans from one that has no codes.

 

I just found this information; "The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady" at https://www.obd-codes.com/p0420

The appears to be the opposite from what I am seeing in the graph. Is this graph what they are talking about what they say "fluctuating wave form?

 

Well, from what I’ve come up with the front sensors are really A/F sensors and should remain fairly steady, their are a few methods to check them but in general, my two front sensors seem to be reacting the same, so although I do not want to rule them out, I think they might be OK for me. As far as cat temps, I think the entering temperature to exiting temperature should be about 100 to 150° difference, I think mine are at about 130. So judging by your graphs, I think you may have a very similar problem to me, which is that one of the rear O2 sensors seems to be bouncing around more than it should be, or at least is not matching the other sensor very well. It is my understanding that the rear O2 sensor should be more or less steady. What’s bugging me about mine, is that sometimes my bank 2 02 sensor (2) seems to be matching and operating fairly closely with the other, but occasionally starts acting significantly different

 

I think I’m just going to start with replacing the downstream O2 sensor and see what happens. I would like to replace all four sensors, but particularly the driver side upstream air fuel sensor is going to be hell to get to.

 

As I read your graphs I see the B2S2 to be very different from B1S2. Where as both of my S2 sensors make graphs similar to each other. From looking at your graphs I think one of your sensors is bad. From looking at mine, they are either both bad or both good. Lets both change ONE of our S2 sensors and see what happens to the graphs?

 

Sounds good. I called the parts store too late today to get my order in, but I’ll call them up tomorrow morning and get new Denso replacements coming for my downstream sensors. I’ll replace just the bank 2 sensor 2 first and record some graphs before touching B1S2.

Will be interesting to see what happens. With any luck I hope to get the new one installed tomorrow. Damn code is driving me nuts.

 

I think you have bad cats

 

Do you think we both have bad cats? Do you see data that suggests that, other than the P0420/0430 codes? Supposed to replace the sensors anyway when you replace the cats, so the sensor swap and to compare the resulting data seems to be a prudent, logical step.

 

I hope not, the bail money for bad cats is ridiculous.

 

Check for exhaust leaks really good around the sensors and exhaust flanges. If the exhaust system is sealed up, you need new converters.

The exhaust temp being similar going in and going out is a good sign they are weak/degraded

There are a multitude of codes related to a/f sensor and 02 sensor performance that the PCM can set if it thinks one of the sensors is not working correctly. If you had a faulty sensor it is highly likely that you would see a one of those codes instead.

Remember, the dreaded p0420/430 is the last code the manufacturer ever wants to see. If those codes appear before 8 yrs/80k then they get replaced under warranty. That's why the cel flashes during a misfire, it's trying to get your attention to avoid a cat failure from raw fuel getting into the exhaust.

The pcm is going to test every sensor in the exhaust up/down/sideways until it is positive the sensors are accurate. Then it will finally get around to testing the cats. If the oxygen storage capacity of the cats are "below threshold " then the codes get set.

Long story short..

-outlet temps should be much higher than inlet

-rear 02s should not fluctuate (the switching of the A/F ratio gets muted/absorbed in a healthy cat by its oxygen storage capability)

-if long and short term fuel trims are stable and less than 10%, then the fuel system has good control (not likely there is a sensor problem any where on the vehicle).

Also, if you have a smoke machine or compressed air, you can pressurize the exhaust pipe and use a spray bottle with soapy water to look for leaks.

Good luck!

 

I concur, I’m thinking I will be replacing the sensors if I replace the cats, so might as well start with easy to get to sensors that appeared to be a little suspect on the diagrams, see what happens.

I just talk to my parts store, they say they have Denso in stock, no waiting so I will head down there this morning and pick at least one up. They are about $35 more each then what I would get from rock auto, so I may just do the driver side only for now.

 

Thank you for the input, and yes, you make good points and you’re probably right, dead cats.

I have checked my system very carefully for exhaust leaks, and actually not too long ago I found a couple of bolts that had just wiggled and fell off and replaced those, which calmed down how often I was getting the codes. But I’ve definitely checked as thoroughly as I could, however when I did my head gasket there was definitely heavy corrosion on the manifolds and although I cleaned as best I could, I definitely have some concerns. No smoke machine, but soapy water and air compressor is a good idea, I’ll definitely do that before taking the plunge for new converters.

You said the outlet temp should be much higher than the inlet temp for the exhaust, by how many degrees would you say? Would you expect the temps to show up on the sensor readings or should I use an IR gun? I will go check now...

 

If you got some relief/results by fixing the exhaust hardware, I would keep going in the direction of a leak!

I'm trying to remember from my last class about cat exit temp.. maybe 100-150 degs? You won't find a data pid for cat temp, that's a diesel thang.

 

Thanks for the input b-r-o, that is good information!!

I changed my Bank 2 downstream sensor. I am not encouraged by the results. Below is the result I got during the test drive. My Fusion smart phone scanner has inlet and outlet cat temp PIDs. So went for a drive on the freeway, 70 mph in cruise. I graphed Bank 2 for cat temps and sensor voltages. Then on the return trip, I graphed the same data for Bank 1 which has the original sensors. I am not seeing much difference.

 

@hemmjo on your data screen, see how the cat temp lines (green/red) are flatlined "above 1000 degs". There is no temp sensing capability in the 02 sensors on our trucks. Your scan tool software is looking for a temp sensor signal but there none available so it just plugs in a predetermined value. If you plugged the scan tool into a Duramax Chevy for example there would be a tangible number in that data slot.

 

Didn’t you say your problem was a P0420 code? Bank 1? Just curious why you changed B2 to instead of Bank 1.

 

Some graphs from this morning....