P0420 Code - Catalyst System Efficiency Below Threshold Bank 1

Use gas conditioner, fuel injector cleaner then fill up with shell high test gas. Now buy a inexpensive diagnostic tool and clear the code. Drive the required driving cycle (not sure exactly what that is), and for me there where no codes and the engine light went out. So stop those blood suckers from robbing you, and troubleshoot yourself. The $79.95 I spent for a diagnostic tool from sears that gives codes and definitions, payed for itself and I figure I saved over 1K.

No I have not replaced any parts but I've had O2 sensor errors before. The wiring connection was durty so when wet I'd get the error and when dry it would clear. I'll try fuel conditioner. I have gotten an error on my 2008 suburban and it says plugged injector, so I put in Sea Foam and it clears up. I'll try the Sea Foam on my 1998 PU and see if it clears the P0420 code.

Performance Muffler in Norman OK reads and clears these lights for free.

I have replaced all o2 sensors and even the catalytic converter when i recieved the p0420 and 430, and that didnt fix error code. Come to find out all i needed to do was a basic tune up, that consisted of changing spark plugs and wires, and really didnt need to change the wires. The problem was, a couple of spark plugs, were faulty. The gaps on the plugs had closed up to where the plugs were getting very little to no spark. So if u have never changed your plugs or even did a tune up i would start there. I paid for a valuable lesson. I work on my own vehicles.

Excellent information! Thanks for sharing

Good information! Thanks for sharing

I have the same codes coming up what kind of car do you have that you changed the spark plugs on i want to try to do the same thing thanks

recently had this code in a 2002 gmc sonoma 4.3L auto 4x2. but mine was a sure thing. the converter was rattling. the packing used inside the converters holds the brick in place. once it broke down it lets air around the brick and the 02 sensor is sensitive enough to detect it. cut the converter off and sure enough the brick is laying there and you can move it around. $60 eastern catalytic universal converter 83166 on ebay. if you can weld.... if not you have to buy the whole y pipes kit which is over $300 and risk breaking the manifold studs removing them. I'd rather weld a cat in than mess with all that. anyone with a rattle in the cat it's a sure thing that it's bad.
btw, 139k miles and the brick was spotless clean. converters don't just plug up if there is no other issues with the motor...all you folks with "plugged" converters are running the vehicles with other issues and never fixing them.

also if you replace a converter they require a "break in". you need to run the engine idle for 5 mins. then increase the rpm to 2500 for 2 min. let engine cool completely. then you can drive it.

hope this helps anyone in the future...

Thanks for the information!

Fixed this on my Tacoma by sealing the leaking flange between the catalytic converter and the pipe (that holds the #2 O2 sensor) that goes to the muffler. Driven over 1000 miles, no troubles. Before I looked, I thought it was going to be an expensive part, but it turned out to be less than $30 for a high grade gasket material and some liquid gasket stuff made for mufflers.

Thanks for the information!!

2005 hilux P0420 code
i have replaced the oxygen sensor x2 and the cat. converter but the cat converter is from a new land cruiser and im still getting the same code needs some help please.... thanks

It should work, but how do you know the catalytic converter was good? also what gas octane are you using? Low octane gas can also cause the P0420 code.

You can't be more specific on sensors. None of your info makes sense. So is it bank 1 sensor 1 or bank 1 sensor 2 that needs to be changed for this code??? White sleeve or black???

The problem is usually the catalytic converter and not the sensors. The color of the sleeves depends on the make, model and year, and some makes have the same color for both sensor. Sleeve color is not an accurate way to describe a sensor.

Hi guys,
I have a 2006 kia rio and have had this code come up,ive been advised of the several issues that could be causing this and i can say that im really not happy to have to pay 1,000+ to have the catalytic converter replaced. Do you have any info on what other likely or common issues there are with this model car to this code just so that i can try the cheaper alternatives before having to pay out money i really dont have.
Thanks in advance.

Try using high octane gas for a few weeks.

I have an 08 Caddilac CTS with the 3.6L DOHC motor. I had a code for cam timing that required the replacement of the timing chains. About 100 miles after I got it out of the shop for that I now have P0420. Could the bad cam timing have anything to do with a bad cat. converter??

It's possible, depends how long did you drove your vehicle with the timing problem. How is the engine performance now with the new timing chains?

I drove it a couple of months before it was confirmed. The performance degraded slowly over the life of the car and it wasn't until the timing chains were replaced that I discovered how much it had degraded. After the chain replacement and the P0420 code appeared I drove the car approx.300 miles and when I got in it this morning the check engine light was off and the code had disappeared. Thank you for the response.

Help. I have a 2013 Dogde Jouney. My daughter made too tight of a turn and hit the back passenger tire on curb, now my check engine light is on and I have the P0420 code.

I have a 2002 Nissan sentra and had a po40 code.I had the cat. cleaned out, and now I can start the car and drive it until it warms up cut it off,then start it up and try to drive it will run but will not shift. I can then cut it off start it up and it will run OK.

Please help

Problems with the catalytic converter should not cause any shifting issues, it's possible that you may have two different problem, one with the catalytic converter and with the transmission.

Nice app