Code PO420, Service engine light?

While it is possible I have only seen it one time and, in that case, it was obvious because the sensor was sending a signal that was out of the range it should have been. What you want to do is select the data from the bank one sensor two oxygen sensor and compare it to the signal from bank one sensor one. What you don't want to see is them tracking together. The front sensor should show a similar pattern to what you see in the short-term trim you posted. You don't want the rear sensor to look that way. Instead, it should only have minor fluctuations. If it tracks the same, then it is likely the converter is bad. What you could try is to add some Cataclean to the fuel and see if it helps. If it does and the light goes out, you can just watch the data later to see if it has started to go bad again. If the cleaning doesn't work, then you will need to replace the converter. For that it depends on the laws where you are, some states allow a universal type unit to be installed, other states require either a factory OEM unit or a CARB certified part.

I'm sending the two videos of the o2b1s1 and the o2b1s2 oxygen sensor readings. Let me know what you think. If you think it's a bad cat converter, I don't want to change it and damage another one. So, I'm wondering if when I changed that defective purge solenoid coil before this failure if it would prevent another failure with a new converter. Do you think an aftermarket converter would work? I also saw where people buy this extended fitting to move the rear O2 sensor out further from the cat so it's not so sensitive.
Thanks for the help my friend.

Yeah that is showing a bad cat. Notice how the two signals look the same? The one from sensor two should be an almost flat line with just a small amount of ripple.
The most common reason for failure are misfires and excess fuel in the converter(s) actually melting and glazing the catalyst materials, next is contamination from oil or coolant being run through the engine that coat the interior with soot or sludge.
As for what parts you can use, that depends on where you are located. Some states are very harsh when it comes to converter replacement. NY for example requires you to use either a factory replacement unit or one that is CARB certified. The fines for using something else are high enough that you really don't want to push it. NY for example has a cascade style fine, say you take in a vehicle that has a V8 in it and has converters in the manifolds plus two more under the car, so you install headers and a full exhaust system. The fine for the first converter being removed is $2,500.00 but the fine for the next is $10,000.00 And for each violation after that the fine increases by 10K per violation. So you removed 4 converters on that vehicle. That could end up costing you a total of $62,500.00 in fines plus the possibility of jail time. Now sat they find that you have 2 of those vehicles and both have the same treatment, you will be paying fines for a long time.
CA is just as bad, and a few other states have similar laws. The "cheaters" are also illegal, and only work on a marginal converter, not on ones that are completely used up like yours.

Just wanted to send two more videos.while driving the truck after resetting the code I was selected to ready test with the scanner. You will see 4 red emission alarms while I drove it with a red light. The engine service light was not on maybe because there were not enough drive cycles.And once again a new oxygen sensor front and rear video. I saw where some people buy this fitting to extend the rear O2 sensor away from the exhaust stream to make it less sensitive. You thoughts on that. I believe the original service engine light came in because of the pure solenoid failure and maybe since I didn't address it right away caused more fuel to damage top the cat. So since that had been replace if I put a new cat on would it not be damaged again or if its something else would it warn me before another failed cat. Thanks

A purge solenoid will dump fuel vapor into the engine and cause it to run very rich. The questions to ask about what might have caused failure - Does it use engine oil? Does it use engine coolant? Has the fuel economy dropped off recently? All three of those can contribute to poisoning the converter. Notice that sensor 2 is hitting the same voltages as sensor 1? That shows the converter isn't working. What you would want to see is the front sensor voltage changing as it is, that is because that system controls the fuel by a simple method, it adds fuel until the sensor says it's rich, then it cuts fuel until it reads lean. It would be like you stepping on and releasing the gas pedal 1000 times a second. The average of that is what the fuel trim corrects. The first sensor controls that. Then the exhaust goes through the converter and hits the second sensor. It looks for the same things, is there excess hydrocarbons in the exhaust? Are those in time with what the engine is doing in response to the front sensor? If it is tracking the lean and rich changes then the converter isn't working as it's job is to burn off the exhaust to make it cleaner.
So, you need a new converter that is legal in your state. The "extenders" only work if you have a marginally bad converter, one where it only throws a code once a month or less. They are also illegal in many states as they fall under "tampering with a pollution control device". In this case it isn't going to work, you need a replacement converter. At least this isn't one of the ones that you need to strip half of the vehicle to get to it.
The GM number is - 12568312 GM also shows it as discontinued however there might still be one out there. Or you could use a AP-Eastern 770421 unit if you are in a CARB state or the AP-Eastern 642543 if you are not in a CARB state. Replacement is going to be Disconnect the rear O2 sensor and heat it up to remove it. Then cut the studs off at both ends of the existing unit unless the nuts are in good shape. Remove the unit from the hanger. Install the new one with new gaskets and tighten the nuts to 26 ft lb. Install the O2 sensor and connect it.

Okay, thanks. If the engine was using a little coolant what would that do to any of the emission items? I don't want to put another $500 converter on only to have it fail again because of the same issue. Would I get another service engine light to tell me what is causing the problem? I already out in a new fuel filter and purge solenoid valve.
Thanks,
Bob

If it is burning coolant, yes that can damage the converter. It is the additives in the coolant that hit the ceramic substrate in the converter and the water bakes off and those additives build up and act like a glass coating over the ceramic substrate. That prevents the exhaust gasses from contacting the metals on the substrate and the converter stops working. The question then becomes how much coolant is it using? If it's say a cup a year, that would take a few years to do damage enough to cause a 420 code again. If it's a gallon every couple months then it would likely damage a new unit in a few weeks.

Okay, thanks.
Would I be able to remove the back O2 sensor just to take a test reading with it out and see if the voltages change breathing fresh air to verify the bad cat? Also since I replace that bad purge solenoid valve if the canister got saturated with fuel would it clear itself up with the new valve by itself.
Thanks,
Bob

Pulling the sensor won't test it. The P0420 code and the changing voltage already shows the cat is bad. The video you posted confirmed that. If it was excess fuel from the purge valve alone it has burnt off by now because it would have been a constant vapor source that is now gone. The canister won't be saturated as the valve draws the vapor out of it. Now that it is operating the system will return to "normal".

Thank you Steve.
I appreciate all the help from you guys.

You are welcome. Let us know what you decide and how it turns out. Might help someone else who has the same problem.

Hello Steve,

Reset the service engine light and wanted to drive truck around some more to verify problem. I agree with you because of the two O2 sensors reading the same the cat is probably bad. However, after about 4 short runs with the truck the service engine light came back on but not with the PO420 code and instead with a PO442 which says evap emission system leak detected (small leak). Did not see any other code. Also 2 months prior I put a high test in truck with Lucas complete engine conditioner. Not Sure if that helped. Down here they want your first born to change a converter. I would try to do it myself but I'm not sure how to get those two rods off that it hangs from in the rubber mount. Don't see any bolts except for the flanges at each end. Would it be worth also running some Cataclean like you suggested earlier? The truck only has 70,000 miles on it. Always did oil changes and maintenance on it. Thanks again for your input.
Bob

It usually takes a bit for a P0420 to set as there are other items that have to happen before it will run the tests. The EVAP leak shouldn't be an issue in that test. I would try the Cataclean and see if the secondary O2 calms down. I sort of doubt it but it shouldn't hurt it.
I just replaced both of the failed converters on a Chrysler at $1,200.00 each. This state requires CARB or OEM only so you pay through the nose.

Okay, thanks.
I guess if that's service engine light starts flashing, I need to shut it down quick right.

The other thing I'm going to check again is inlet and outlet temperature. The last time it was cooler in the front than the back which told me it was working by about 200 degrees.

That temperature is very low for a correctly working cat. That would be one item that might give you a hint if the Cataclean worked, if the temperature goes up after the treatment it likely cleaned out some of the crud and could give you some extra time. Yes on the flashing CEL, that is generally telling you that something is trying to wipe out the cat.

Thanks Ken,

I'm going to take the cat temperatures one more time (front and back) after it warms up and send them to you. How do I find the cause of the PO442 code (evap emission system leak detected) (small leak) if the cat code never comes back? Also I may still change the cat and found a big difference in the two prices from different places for the same part. Walker # 15823. Could it be the same item?

If they will actually fill that order at that price and it's legal in your state, then I would order 2 and put one up for sale to get your money back.

As promised, I took the readings several times in the front of the cat and behind and these were my results:
Test 1- front 352 back 542
Test 2- front 410 back502
Test 3- front 434 back 517
What do you think?

Still real low, a working cat should be up around 800 - 1100 degrees depending on engine load.

Okay, thanks.

Okay, going into the 5th run the service engine light came back up with the PO442. I wrote down the list of possibilities that the scanner recommended. What's the best place to start. I already put a different gas cap and no help.

A very small leak is this size or smaller - o very seldom is it the cap. I would get a smoke machine and set it up. Let it run a couple cycles and start hunting. One of the common leaks is on top of the tank where the pump housing cracks. The nest is the vent valve and the next is a bad tank pressure sensor.

So before it had the po440 which was saying cat low efficiency. On the 5th drive like I said above the po442 came up by itself only saying evap small leak. So can I assume the cat converter is ok or will it need more than 5 drive cycles to find out. Also can I drive without damage to the engine with this po442 code for now until I find the small leak. Maybe they engine conditioner and high test cured the cat code.
Thanks for the recommendations.

It will take a few drive cycles to show if the converter is functional or not. With the light on for the leak it likely will not run the cat test anyway. So that may still come back once you get the EVAP leak solved. The EVAP leak won't cause an issue other than the light being on and it may block other tests from running.

Okay thanks, saw.

Where would you inject the smoke machine in the 2003 chevy s10?

Pull the line off the purge solenoid and inject the smoke there.

Purge solenoid is buried up behind this 4 cyl. Engine. I had to jack it up and take the right front wheel off, fender skirting and still could not see it and could only touch it with one hand. I am still not sure when I changed it if the purge solenoid valve vacuum line was secured enough. Horrible vehicle to work on. Need to find a different area to inject it. Can't low pressure air from a compressor find a leak with spray soap.

The problem with using anything over a few inches of water in the EVAP is that you can damage the pressure sensors and the valves. The typical solution is a BBQ grill regulator on the home built smokers. That drops the pressure down to just under a half of a psi. It's enough to get the smoke in and show the leaks.
To test the EVAP you need to get the smoke into the lines for the system. On some GMs there is a green capped service port for testing but those are somewhat hit or miss depending on the engine, model, and build date. If it has one you can connect there.

I need to replace my transmission fluid on my 2003 chevy s10 2.2 liter engine. Can I suck most of the fluid out of the dip stick location as I'm too old to crawl under the truck?

Even though this is the transmission we like to keep each question as a different one to make searches easier. We ask they each question be kept apart. But on that truck, if you park it with the left side barely higher than the right you can get most of the fluid out of the pan.

By sucking it out through the dip stick? Any idea what I could buy to suck it out. I'll keep questions separate next time.
Thanks

Well you can get units like this one in multiple places https://www.harborfreight.com/23-gallon-manual-fluid-extractor-62643.html . if you don't mind pumping the handle. Some parts stores have them as loaner tools.

Hello Steve
A bit more info on the 2003 S-10. Reset code and driving it with the high test gas. It idles ok and accelerates ok up to about 45mph. At that point if I step on it the engine hangs at that point. If I back off and step it down real slow it will try to pick up. When I got home in the driveway in park I slowly increased them engine speed and at 4000rpm its stoped and started to drop off. Then back up to 4000 and then it would not go past that point. Whats your thoughts. Im going to make some more trips and see if I can get a code to cone back up and let you know. Did not change Cat yet

That description could be a partially clogged converter. It's possible to check that through back pressure testing. I do that with a simple fuel pressure gauge and by drilling a small hole above the converter and driving in a short piece of brake line. Then attach the gauge to that. The other test is to just pull the front O2 sensor and see if it runs better.

Okay, thank you sir.

Let us know what you found.

Okay. Going to be awhile as I'm having some medical issues and can't crawl under my truck. Took many recent surgeries.

Sorry to hear that. We will still be here though.