The Trainer #118: The REAL Cause Of P0420/P0430 DTCs

the dreaded po420 and o430dtc is the catalytic converter efficiency below threshold these two codes are among the top 10 dtcs that technicians face on an everyday basis and while the name might imply that the converter has failed odds are it's not the ultimate cause of the failure learn more in today's edition of the trainer [Music] today's edition of the trainer is brought to you by autel be sure to visit them at www.autel.com [Music] while the p0420 or o430 diagnostic trouble code can indicate a catalytic converter that has outlived its useful life there are a few things you should understand before you order the replacement let's start with the three ways that a catalytic converter can fail this is usually caused by any factor that affects the engine's air fuel mixture and the resulting exhaust or feed gases being sent to the converter in order for the cat to work efficiently these feed gasses must be kept in a very narrow range expressed in lambda even slight variations will cause the converter temperature to rise significantly converter poisoning is a common cause of premature converter failure poisoning occurs when the substrate is coated by a foreign substance usually oil or coolant and is then insulated from the exhaust gases structural damage can be physical damage like that caused by road debris striking the housing and it can also be things like stripped oxygen sensor threads thermal shock to the converter and metal fatigue at mounting points or welds while the po420 and po430 trouble codes may indicate a converter that's outlived its useful service life there are a few things to ask yourself before replacing the converter number one is the converter really bad number two if it is what caused the converter to fail and if the converter has passed and it's okay well then we need to know why did the ecm set this false code take the vehicle for a test drive pay attention for any abnormal noises that may be coming from around the area of the converter pay attention also to how the vehicle responds is it sluggish does it lack throttle response does it have an overall feeling of low power any of these can be caused by a restricted exhaust that is a result of a melted or broken substrate the next step is to connect your scan tool and verify the presence of the p0420 and or the po430 dtcs and make a special note of any other dtc's that might be recorded in the ecm any dtc's or conditions that you find that either impact the emissions level of the vehicle or the sensor's ability to provide correct information to the ecm can skew the ecm's test of the converter so make sure that you repair these conditions and dtcs first then re-run the catalytic converter monitor before you replace the cat while the scan tool is connected take a look at the fuel trim data pids do they indicate a system that is biased a bit lean or rich as i said earlier the feed gases going to the converter have to be maintained within a very narrow lambda range or converter damage could result on vehicles that use a conventional oxygen sensor before and after the catalytic converter the ecm monitors the inputs from these two sensors to assess the state of health of the converter it expects to see the front sensor switch normally while the rear sensor should remain a fairly stable output if the rear sensor's signal mirrors the front sensor the ecm may determine that the converter is not doing its job now any other factor that could result in these same signals like a bad sensor for example could cause the ecm to set a false code and the converter's just fine now in this vehicle it uses an air fuel sensor upstream of the catalytic converter in this case the voltage is going to change very little so it may help to look at the current output instead but be careful make sure you read up on the ecm's protocol to make sure that you're looking at the right data next let's put the vehicle up in the air and inspect the exhaust for any signs of physical damage or obvious leakage here's a tip that i learned from trainer mike becker it's a low-tech way of finding those pesky exhaust leaks and it takes advantage of your shop vacuum simply plug the hose of the vacuum to the outlet side insert it into the exhaust and then seal it around the pipe turn the vacuum on and now you're pressurizing the exhaust system next all you'll need is a mixture of dish soap and water and spray the exhaust down liberally looking for the air bubbles that indicate the leak source common sources of air leaks into the exhaust that can skew the ecm tests are damaged flex pipes and stripped or damaged sensor threads you can even use a thermal imaging camera like this autel ir 100 to see the converter in action start the engine and allow it to reach operating temperature then check the temperature of the converters front weld ring depending on the size of the converter most converters light off around 350 degrees fahrenheit and are fully lit around 500 degrees fahrenheit and this temperature can be tested at the front weld ring if this temperature is never reached the converter may be faulty or it's not receiving the right feed gas mixture from the engine the temperature of the converter's rear weld ring is directly related to the amount of work the converter is doing under normal conditions it may reach temperatures as much as 150 degrees fahrenheit higher than the front weld ring if the rear well ring is hotter than it should be it's a good indication that the feed gasses are outside of that very narrow range i talked about it may be lean rich or there could be contaminants in the exhaust stream and if the rear weld ring is colder than it should be well that can indicate a catalytic converter that has failed and it's unable to light off or it could also indicate an emissions related problem maybe cat poisoning because of those contaminants a bronze blue rainbow discoloration of the shell typically indicates elevated temperatures and overheating of the converter typically converter temperatures will not exceed 1200 degrees fahrenheit on a properly running engine but periodic operation above 1600 degrees fahrenheit can reduce the converter's efficiency by damaging the precious metal coating on the substrate now if you suspect that there's damage to the substrate you may get a clue by removing the oxygen sensor and using a bore scope like this one the autel mb480 to get a closer look just one word of caution the substrates when melted generally melt somewhere near the middle and may not be readily visible if any of the checks that we've done so far have proven that the converter has failed we still need to know why it failed was it old age or is there another cause that we have yet to determine and we need to correct and if the converter is good we also need to know what is it that the ecm saw that it didn't like is there some fake input that it's receiving that's misleading it when it's making its tests now we know we need to keep those feed gasses in a very narrow range and one tool that we can use to help us determine if that is indeed the case is the conventional 5 gas analyzer when using a 5 gas analyzer keep in mind that high hc emissions indicates unburned fuel high co levels indicate partially burnt fuel or oil high nox levels are normally caused by high combustion temperatures and pressures slightly lean air fuel mixtures or excessively advanced ignition timing now if you do see five gas results that are out of whack consider that we're focusing on hc co and nox if hc and co are low but nox is high well odds are that's not a result of a bad converter that's usually something else but if you see all of them high you can suspect that the converter is not doing its job or it's not getting the fee gas as it's supposed to get and that's the case we want to take a close look at engine drivability items is there a misfire is there a fuel trim issue things along these lines one way that you can determine if all the cylinders are contributing their fair share is by using your thermal imager and looking at the temperature of each exhaust runner usually if there's a cylinder that's not carrying its weight it's going to be colder than the others so remember when you're diagnosing a po420 or o430 diagnostic trouble code you need to consider a few different things first is that converter really bad and if it is what caused it to go bad and if it's not bad what is it that tripped up the ecm in the first place if you don't correct these underlying causes you're just going to have a dissatisfied customer and potentially an expensive comeback if you'd like to learn more about any of the autel tools that i used in today's video please log on to www.autel.com and as always thanks for watching [Music] you

Channel: Motor Age

Views: 993,093

Keywords: motor age, the trainer, automotive repair, car repair, auto how to, how to fix my car, auto tech, auto technician, auto service professional

Id: zQ8BXAwK-QY

Length: 11min 57sec (717 seconds)

Published: Fri Oct 01 2021