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Juan Crespo
Juan Crespo, Tech Trainer
Category: Toyota
Satisfied Customers: 1516
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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PO420 DTCI have a 2005 Toyota Camry with a PO420 code. I

Customer Question

PO420 DTC
I have a 2005 Toyota Camry with a PO420 code. I need assistance diagnosing and repairing this issue. I am mechanically inclined, have Actron CP9670 Scanner and Multimeter. Please only reply if you are a Certified Mechanic with hands-on experience with this vehicle along with OEM knowledge base. Sorry to say that I've used this service in the past with mixed results. I have had both expert professionals AND hacks respond to my requests for assistance for vehicle repair. Lets not waste each other's time - please only respond if you can work at a productive level.
Submitted: 8 months ago.
Category: Toyota
Expert:  Dave Nova replied 8 months ago.
The P0420 code sets when the catalytic converter is no longer efficient at removing hydrocarbons from the exhaust gases. The computer monitors O2 sensors before and after the catalytic converter. If the downstream O2 sensor readings too closely mirror the upstream sensor readings, then the converter is not doing its job. You should check the exhaust system to make sure there are no leaks ahead of the converter. Beyond that, the only fix is to replace the catalytic converter. Some people try in vain to replace O2 sensors, but it will not fix the P0420 code. Make sure to use a Toyota converter (or OEM quality). We see too many people replace the converter with the cheapest replacement part, only to have the code come back in 6 months to a year.
Customer: replied 8 months ago.
Thank you.
This vehicle has an air/fuel sensor on the exhaust manifold, then two O2 sensors - one in front of the cat the other in back of the cat. The car has approx. 225k miles. I am seeking detailed instructions on how to test the sensors. I've read that the O2 sensors have a useful "service life" and at 225k I think it prudent to test if possible. Can you direct me on how to test these three sensors? I have also found mention that a bad or dirty MAP can trigger the PO420 code. Is it work getting hold of some CRC MAP spray cleaner to clean the wires ? 0 Thank you
Customer: replied 8 months ago.
Meant to type "is it worth......" (cleaning of MAP)
Expert:  Dave Nova replied 8 months ago.
The MAF sensor can change O2 sensor readings, but will not affect the P0420 code, since the computer is just comparing readings of front vs. rear sensor. If an O2 sensor is bad, there will be codes for that sensor. If the only code you are getting is the P0420 code then the sensors are okay and the catalytic converter is the faulty part.
Expert:  Dave Nova replied 8 months ago.
If your scan tool has live data readout, you can check the functioning of the O2 sensors by watching output data with engine running. Sensors before the converter should fluctuate above 600 mv and below 300 mv. Sensor behind converter should stay closer to center range (450 mv) Too much fluctuation and the P0420 code will set.
Customer: replied 8 months ago.
Yes - my scanner has live data readout. I will check this tonight but I don't understand when you indicate
"Sensors before the converter should fluctuate above 600 mv and below 300 mv"
Shouldn't the sensor fluctuation be BETWEEN two readings? - I don't understand "above 66mv" and "below 300mv"
ALSO - the Toyota CAT is crazy expensive. I understand what you say about not being penny wise and dollar foolish here but what lower cost aftermarket CATs offer lower cost with OE type reliability?
Thank you
Expert:  Dave Nova replied 8 months ago.
The O2 sensor range is 0 mv to 1000 mv. Lower readings indicate lean and high readings indicate rich condition. When accelerating, 800 - 900 mv is common. When idling with the engine warmed up, the sensor readings will be constantly fluctuating. You should see the reading go below 300mv and above 600mv when it is fluctuating at idle. Hope this better explains it.
Expert:  Dave Nova replied 8 months ago.
As far as catalytic converters go, you do generally get what you pay for. If you don't want to shell out the big bucks for the Toyota unit, look for one with the ECO-III designation.
Customer: replied 8 months ago.
Eastern catalytic has ecoIII
they show one called MANIFOLD UNIT TUBULAR VERSION AND ANOTHER called REAR UNIT - FEDERAL EMISSIONS.
Does this vehicle have two CATs - one that's part of the exhaust manifold and the other that is under the car connected to the exhaust pipes ?
I also see similar at rockauto.come, autozone.com, etc.
Expert:  Dave Nova replied 8 months ago.
Is your Camry a 4 cylinder model, or V6?
Customer: replied 8 months ago.
It is the 2.4L four cyl.
Customer: replied 8 months ago.
The exhaust manifold has a "round" shape that looks like it houses something inside.
Customer: replied 8 months ago.
The Air/Fuel sensor screws in right on TOP of that manifold - not the side
Expert:  Dave Nova replied 8 months ago.
The catalytic converter is housed inside the lower portion of the exhaust manifold.
Customer: replied 8 months ago.
Wait a second here..... all of the parts sources show a "tubular on manifold" AND a "rear" (either Fed or CA emissions)
For all sources BOTH are listed as CATs. This is a three way CAT - are there actually two CATs on this vehicle ?Take a look at any online parts source - you will see these.
Expert:  Dave Nova replied 8 months ago.
The camry has two catalytic converters. Both are considered 3 way converters. The P0420 code sets when the primary converter (in manifold) is failing. see attached diagram
Customer: replied 8 months ago.
I ask that you please allow another Just Answer mechanic to take over this case. I am not getting the level of detail that I asked for and do not wish to continue with you.
thank you
Expert:  Dave Nova replied 8 months ago.
That will be fine. Good luck with your repairs.Dave
Customer: replied 8 months ago.
Does this automatically become open to others ?
Expert:  Dave Nova replied 8 months ago.
It will be open to others as soon as I opt out. Give me about 30 seconds to complete that.Dave
Customer: replied 8 months ago.
I would like Sky Vision to respond to this question. I have worked with him before and he provided expert advice
Expert:  Juan Crespo replied 8 months ago.
Hi there.I'm a retired tech trainer who actually taught this class to Toyota techs at the Toyota training facility at J Sargeant Reynolds Community College in Goochland, VA. As such, I can offer you the same level of technical detail as those techs got.Here are some facts about code P0420 as it pertains to the 2AZ-FE engine: The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its' efficiency. The first sensor, an Air-Fuel ratio (A/F) sensor, sends precatalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S), sends post-catalyst information to the ECM. The ECM compares these two signals to judge the efficiency of the catalyst and the catalyst's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown. If the catalyst is functioning normally, the waveform of the heated oxygen sensor slowly switches between RICH and LEAN. If the catalyst is deteriorated, the waveform will alternate frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable. When running the monitor, the ECM compares sensor 1 signals (A/F sensor) over a specific amount of time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors (for the rear oxygen sensor, the ECM uses the output voltage signal length). If the oxygen sensor output voltage signal length is greater than the threshold (threshold is calculated based on the A/F sensor signal length), the ECM concludes that the catalyst is malfunctioning. The ECM will turn on the MIL and a DTC will be set.So, to clarify:There are only two sensors in this system, one is an Air/Fuel sensor located on the exhaust manifold upstream of the catalytic unit and the other is a heated O2 sensor located downstream of the unitThe exhaust manifold and catalytic converters for both banks 1 and 2 are built and sold as a single unit - Eastern part# ***** would be the correct replacement for the Toyota factory unit.Please let me know if you have any other questions or if you would still like to work with another expert on the site.Best Regards.
Customer: replied 8 months ago.
Thank you Juan - what is the bank1 sensor2 for ?
I thought my car has three
1. Air/fuel (mounted on top of ext. manifold
2. O2 sensor = before CAT on exhaust pipe under floor board
3. O2 sensor = after CAT on exhaust pipe under floor board
Do I have this wrong ?
thank you
Expert:  Juan Crespo replied 8 months ago.
They say a picture is worth a thousand words...
Customer: replied 8 months ago.
Thank you Juan - I don't see the third sensor in this diagram. Also this diagram is not an accurate representation of my exhaust manifold. Images to follow
thank you
Customer: replied 8 months ago.
Juan - attached are pics of my actual setup (this is from the car I'm working on).
Shown are:
air-fuel sensor bank1 sensor1
O2 sensor bank 1 sensor2
O2 sensor bank 1 sensor3
First question is why do the non-OE replacement exhaust manifolds NOT have the air-fuel sensor mounted on the top like mine ? They all see to have it on the side.
From what I understand from your first response the PO420 code indicates that the CAT in the manifold is bad. All of the parts for this repair are costly so I'd like to diagnose this issue to the fullest. Is there a way to easily determine if the sensors are functioning properly and not themselves faulty causing the PO420 code? I have an Actron CP9670 scanner and a multimeter that we can use for testing. While not expert with either I can follow directions.
ALSO - its still not clear to me what the function of the O2 sensor - bank1 sensor3 is. Is it possible that this sensor is faulty causing the PO420 code and if yes how can be test this one?
thank you
Expert:  Juan Crespo replied 8 months ago.
Sorry for the late response - I usually don't logon until 2PM AST.Those pics you uploaded indicate you're working on a Partial Zero Emissions Vehicle, which is something we don't see a lot of in states other than California. Is this a California car?
Customer: replied 8 months ago.
Juan - attached are the under hood sticker and the VIN (dashboard sticker)
Customer: replied 8 months ago.
BTW - I like in NY - purchased the car from a Toyota dealer in NY (used) Not sure why it would be "California" car.
Customer: replied 8 months ago.
Meant "I live in NY"
Expert:  Juan Crespo replied 8 months ago.
Thank you for those pics. The underhood sticker confirms it is a Partial Zero Emissions Vehicle (PZEV) built to conform to California emissions regulations and therefore legal in the state of New York (CA and NY have their own similar emissions regulations).These PZEVs engines use a different strategy to detect deterioration in the front catalyst:The ECM calculates Oxygen Storage Capacity (OSC) in the catalyst based on voltage output of the heated oxygen sensor 2 while performing the "active air-fuel ratio control" instead of the conventional detecting method which uses the locus ratio.The OSC is an indication value of the catalyst oxygen storage capacity and is used for representing how much the catalyst can store oxygen. When the vehicle is driving with a warm engine, the "active air-fuel ratio control" is performed for approximately 15 to 20 seconds. When it is performed, the air-fuel ratio is forcibly regulated to go LEAN or RICH by the ECM, and if a RICH and LEAN cycle of the heated oxygen sensor 2 is long, the OSC will become greater, and greater OSC basically capability of the catalyst are mutually related, the ECM judges if the catalyst has deteriorated based on the calculated OSC values.All of which means that we would need both a scope and a capable scan tool to diagnose this issue if the expected results are to be 100% accurate. I looked up your scanner online and it is not capable of doing what we need. Can your meter read O2 sensor voltages fluctuating every 100 milliseconds or so? Please tell me brand and model if you don't know.
Customer: replied 8 months ago.
I am confused Juan - you said that you looked up the scanner online and "it is not capable of doing what we need" but then you ask.....
"Can you meter read O2 sensor voltages fluctuating every 100 milliseconds or so? Please tell me brand and model if you don't know".
Again my OBDII Scanner is an Actron CP9670 - here is a link to the scanner web page that shows capabilities.
https://actron.com/content/autoscanner-live-data-color-screen (link to Acton scanner).
I have also attached the user manual.
Please advise - thanks
Expert:  Juan Crespo replied 8 months ago.
Sorry if you're confused. You posted "I have an Actron CP9670 scanner and a multimeter that we can use for testing". I looked up the scanner and found it is not capable of doing what we need it to do. Now I'm asking about your multimeter; is it capable of measuring individual voltage fluctuations occurring every 100 milliseconds or so?
Customer: replied 8 months ago.
Now I understand - I don't know.... I know how to use the multimeter for basic tests.
I will get the model number of the multimeter and also the user manual if I can. If the one that I own can't do what we need I should be able to get my hands on one that does.
Customer: replied 8 months ago.
Just a note - from what I gather the info that you've provided is quite high level. Now that I am introduced to this knowledge I simply wonder how the average mom and pop garage can expertly service a vehicle such as mine (one of the most common cars out there). Hence the "Shotgun" method that most shops use. A little while ago I spoke with a mechanic friend of mine and he cautioned me against assuming that the CAT was bad. He has his own interpretation of how to diagnose the issue but my gut told me his was a very generic approach. What I did take away from that discussion was a faulty sensor cause a CAT to be misdiagnosed and the best approach is to test the sensors before laying out the cash for a CAT.
Expert:  Juan Crespo replied 8 months ago.
I agree in that testing the sensors is not only the best procedure, but also the only procedure that will result in an accurate diagnosis - the thing that most people miss is that the testing strategy or methodology is not the same for all vehicles.
Customer: replied 8 months ago.
Here is a link to the multimeter that I own
Still trying to find the user manual - link to PDF on their site is dead.
http://www.gardnerbender.com/en/gdt-311
Customer: replied 8 months ago.
Found the multimeter manual - (attached).
Expert:  Juan Crespo replied 8 months ago.
I just looked at the specs for your meter and found it can't do what we need it to do either. So, at this point, it looks like my technical knowledge and guidance alone are not going to be sufficient to do what you want to do with the tools you have.Regarding getting expert service, any shop who employs qualified technicians who have the correct tools and access to technological information (Alldata, Mitchell, etc.) should be able to diagnose and repair this kind of issue.
Customer: replied 8 months ago.
By mom and pop I mean those shops that don't know how to read a manual ! There are lots around my area.
So I need a specific type of multimeter. I can probably get one - what am I looking for? Please describe so that I can pass on to my supplier.
ALSO - - Have a friend at an auto parts store that can get me sensors and he allows me to return them is not used. If I wanted to try just swapping sensors which one would be your "best guess" to start with? The Air/Fuel Sensor or the Bank1 Sensor2 sensor. I understand that this is not exact science but I would imagine that you have experienced this particular failure in the past and from experience have seen a common failure to certain components.
Expert:  Juan Crespo replied 8 months ago.
In my experience, gasoline quality is what kills these converters. The sensors are just doing their job and reporting what they see.I don't like guessing, but if I were to do so, I'd say there is nothing wrong with the sensors, you just have a bad cat.
Expert:  Juan Crespo replied 8 months ago.
My research shows this cat will fit your application - click here to see. RockAuto has it listed for $464.79 with a $50 discount via debit card - click here to see.
Customer: replied 8 months ago.
Interesting - gas quality?
Do you mean the difference between regular and .... for example Sunoco's Ultra ?
Expert:  Juan Crespo replied 8 months ago.
No, gas quality as what's in in it. Not octane rating.I've enjoyed our interaction, but the powers-that-be who run this site don't really like it when we spend too much time with one customer - understandably, they'd rather have us answering many questions from different customers so they'll get more revenue.Is there any thing else I can do to help at this time? If not, and you think my efforts so far are worthy of a positive rating, then kindly accept my answer now.Best Regards.
Customer: replied 7 months ago.
Juan - just an update.
You were mistaken that this is a PZEV.
I contacted Eastern Catalytic Converters tech support and they determined that I have the "super ultra-low emissions" setup.
This is determined by the engine family on the emissions sticker. My 05 Camry has to different exhaust manifolds. The one that I have (the SULEV) if not available aftermarket.
Customer: replied 7 months ago.
...actually "TEST GROUP" on emissions sticker not engine family

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