all hail Scotty---2005 Ford Escape XLT 3.0, 260K, bought from trusted neighbor after stroke for a grand. I got OBD PO420, says threshold failure bank 1, goes up steep hills at 20(!!) mph. I replaced one of three cats(bank1, left side, half the V6) didn't cure problem. Now I replaced fuel filter (air filter clean) gonna go test it. No smoke, idles good, goes through gears (auto tranny) normally. Steeper hills suck. Car is a 4+ out of 5 for looks and maintenance, all electrics, in and outside perfect . IM late 60's any thoughts? Replace ALL cats? (Engine light is out now)

Good morning everyone. I have a 2002 Toyota Camry 3.0 litre 1mz-fe. It has 78K miles and a automatic transmission. I recently purchased this car and have an OBD code I can't diagnose! Code reads PO420 I recently replaced spark plugs, air filter, cleaned my MAF sensor, and fixed a vacuume leak in front of the throttle body, and replaced a stuck PCV valve that sucked some oil. Live data shows bank 1 and 2 oxygen sensors with a negative fuel trim of around -7.5 short term. Long term is a around -9. Live data also shows the code was tripped at around 60mph. Car runs good; only revs a little over 2k RPM in mornings on cold start then warms up and stays steady around 700rpm. Also notice a slight unburned gas smell on startup. What do you think is the problem? Thank you!🤙🏻

New fuel injectors.  If you keep letting it run lean, you could burn a piston.

Dear Scotty, I have a 2003 Toyota Matrix 1.8 L automatic.

With error code P0420 “Catalyst system efficiency  below threshold bank 1”

does this mean my cat is clogging up, or my O2 sensor is failing? 

The check engine light came on a few days ago when when I was driving in  torrential rain. I thought it might be possible something just got wet. after not driving a couple days, the check engine light is off, but it’s throwing this code.

should I erase the code and keep driving? Should I do anything else as a precaution?

P0420 on a Ford focus Se 2017.

I've already replaced the O2 sensors. There's no performance issues but code still appears.  I purchased the car at 52000 miles in 2019 and right now I have 81000 miles on it  Could the catalytic converter really go out that soon or is that normal?

Scotty hello! I got a 2000 Subaru Impreza RS 2.5 liter, I got a Check Engine Light with Code P0420, what should I do?

Hello,

I have a 2003 Toyota Sequoia, 200k miles. It had a P0420 (Bank 1) code when I scanned it earlier today. I know typically this would require a new catalytic converter, but while looking at the live data a little while ago, I noticed that the O2 Bank 1, Sensor 2 sensor is flatlining at 0.035V, pretty far below the 0.1V-0.9V the other 3 sensors are performing at.

Is it possible that this sensor could bring up this code? Other than the P0420, it has no other codes. The vehicle runs extremely well, which makes me question whether it is truly the cat or not. There is no shaking at idle, no sulfur/rotting egg smell out of the exhaust, no dip or loss in engine power or performance.

If anyone could shed some light on this issue, it would be amazing. Thank you! 🙂 /p>

My 2008 Dodge Grand Caravan catalytic converter gets burnt or at least gets an OBD code P0420 every time a couple months after replacement.

I'm assuming something else is the cause ? 

I replaced the spark plugs and wires, and the only OBD code is the P0420. 

Any thoughts would be appreciated. 

I have a 2002 hinda with code p0420 I have tried cat clean didn't work I going to try a o2 sensor spacer which would be the best on and do they work I live in wv so no emissions test 

I have 170000 miles and I have p0420 

I'm also getting bad gas mileage 

How do I know if my O2 sensor is bad in which one

It's probably the heater circuit in the 02 sensor at the exhaust manifold.  Just spring for a new one and call it a day.  About $45 at Autozone.

I have a 1999 toyota 4runner V6. I bought it with no exhaust 1 year ago and got a brand new cat and both oxygen sensors. It was fine for a year and I recently got p0420 catalytic converter below threshold bank 1. 

My bank 1 sensor 1 oxygen sensor voltage stays at a steady .65 volts and bank 1 sensor 2 fluctuates rapidly from .04-.83 volts.

Is the sensor 1 supposed to fluctuate as well? Or is that supposed to remain steady.

I don't see how the cat could've gone bad in 1 year, I hadn't been running lean or anything. It is a good magnaflow cat. 

 Why do I get a check engine light for P0420 after replacing my catalytic converter twice ?

2010 Honda Civic Lx

I had my mechanic replace the catalytic converter twice. Replaced both upstream and down stream oxygen sensors. Checked for exhaust leaks. Replaced the computer (this was for another issue but I felt it could not have hurt to try to see if that would have removed the light). 

P0420

2001 toyota solara 3.0 1mzfe

I had this code for some time, it happen when the car had misfires due to the spark plugs wires being place wrong. Its says bank 1 but i don't know which cat it is. The rear of the motor bank 1 precat or the last cat that its in the center of car. 

I have a 2011 Cadillac CTS Coupe getting a p0420 code with no check engine light.  The check engine light does come on when I start the car so the light does work. HELP

Hi, 

I have a 2005 Toyota Tacoma V6 4.0 4x4 Crew Cab with 235,000km (145,000 miles) showing codes P0430 and P0420 at the same time.

I have since tried catalytic converter cleaner as well as replacing a very rusty muffler (needed to be done regardless) hoping that either the cats needed to be cleaned a bit, or that the muffler was allowing air to mess with the O2 sensors causing the codes to trip.

I cancelled the codes but they have reappeared as it seems that I haven’t solved the issue.

I am thinking I should replace the O2 sensors as the next cheapest option before biting the bullet and replacing the catalytic converters. What do you all think?

• I just shot but you could try oxygen sensors sometimes they can go bad and give skew data. Don't more often it is bad catalytic converter

vw polo 1,2 12v 3cyl 2003

60000 miles.

was sitting in garage 10 years before i got it (iam driving it 4 years since i got it)

scotty i had p0420 then i have my catalyst removed to solve it (opened it and remove the inside stuff and close it) and i have check engine on now again (with codes for o2 sensor circuit, evap and fuel presure) those codes come and go sometimes...+ i did install an o2 spacer-adaptor to fool the downstream sensor. and i changed the upstream sensor with an ngk one (new) and sometimes i got code for it too..i did a test to the upstream one and the voltage was 0.2 max (the downstream works fine) while driving and the car was warmed up.the freeze frame showed once hapened on 2000 rpm second gear and the other time 3000 rpm 5th gear + the fuel system 1 was OL and coolant temp 185. any idea what can be? 🙂 thanks ! i wish i could come to you and fix it :S oh i forgot to mention i have a k&n air filer inside the stock beaty cover it have. + i cleaned injection system and throtle body and air sensor (maf or map i dont remember really) the car services are on its time and earlier + i put the best spare parts and fluids etc etc.

I have these two error codes on my 2012 automatic Hyundai Genesis sedan with 103,000 miles and don’t want to pay 160$ to get my car tested and want to know if the codes I’m getting are to get my cats replaced or if it’s just a simple O2 sensor.

P0430 and P0420 error codes

basicaly my problem after all these i said is that i have (right now) only p0130 code active while ive changed recently this o2 with a new one and iam trying to figure why..(plus it works with 0.1 volts and OL fuel system status 1 when its warmed up and driving on the highway.and i dont think its the air filter ''case'' that has a sucking hole or something and my exhaust has no leaks.

Just found what it is.. its because the sensor 1 and 2 have the same data (cause gutted cat) and that cant be.. so the sensor 1 working but the other doesnt correct something so it thinks the sensor 1 is gone.. soo the car working fine with air fuel ratio its just the DTC (sensor 1) that showing sometimes. meh (o2 spacer doesnt always work 100%)

I have a 2010 Volvo XC60 T6 (turbo 3 Liter) AWD with 115K miles, I am first owner.

The CEL first came on at 60k miles and shows code P0420 (Catalyst system below Efficiency Threshold (Bank1)).

It is mostly on, but then intermittently goes off when the fuel gauge reads 2/3 to 1/2 full, and then comes back on again after a short time. My Volvo guy (using Volvo diagnostics) says it is most likely the catalytic converter, but how can it fluctuate between good and bad? 

I have used cleaners with success to get it past its emissions test, but would like the issue resolved, as when the CEL is on it masks any possible other issues that may occur.

I still use the OEM gas cap (tried a replacement without any change), and have tried various system cleaners, but nothing permanently cures it. 

The car runs fine, no misfires, plenty of power, no nasty bad-egg smells. I tried premium gas for several months with no change, and back to regular

Thanks

Well this guy has the same car and he fixed his. Worth a read anyway. 2010 XC60 T6

Hi Scotty, I brought the Thinkobd 100 on your recommendation and came up with a P0420 code. It also says That the Catalytic system elliciencybelow threshold Bank 1. The car is a 2003 crv. I checked the engine air cleaner and it need s to be replaced. Will do this along with cabin filter . I’ve seen your video on the mass air filter cleaner and throttle body cleaner. I don’t see a similar unit on my engine though it or something similar should be there. Any ideas of the proper way to proceed?

https://postimg.cc/BLJWYzJC

What might this mean? 2005 toyota camry 170k miles

You need to find the reason for the CAT deficiency.  Burning oil or coolant, overly rich air/fuel mixture, dirty MAF sensor, air filter, etc.

The codes for inefficient cat operation is occurring from a problem farther upstream of the sensors.  Are you burning any oil, is the fuel trim within specs, etc?  Are you losing coolant from the reservoir?  Has the PCV valve been changed out in the last 17 years?

Hey Scotty,

I have 2012 mitsubishi lancer 2.0L 4 cylinder engine with 119,000 miles. Recently i have been getting the code p0420, I have reset the code 4 times and have been able to go around 300-500 miles before it comes back. I hooked up a scan tool and the freeze frame data each time shows that the gas sensor has failed at an interval. I have tried cataclean which did cause the code to go away but it came back, should i try lacquer thinner, replacing the sensor, or replacing the cat?