Just had CEL come on. Error code P0420

I just had my CEL come on. I checked it with my OBD scanner and code P0420 and P0420 P came up. Sighs. I don't have thousands of dollars to have my Catalytic Converter replaced. How do I find out for sure that is what needs to be replaced? Any thoughts on what to do? Can I just reset the code and see what happens? Will not replacing the Caty kill my engine? Thanks.

 

Could be an 02 sensor which is pretty cheap and easy to fix. May be an exhaust leak as well.

Seems a few people have run a can of seafoam through, and that took care of the issue.

 

I have replaced both O2 sensors in the last 6 years or so. How do I know for sure if it is that before I change them and find out it is not that?

 

catalytic converters don't go bad on their own. They are killed by rich fuel mixtures or contaminants (oil, silicon, coolant, etc). If you don't or didn't have any of these issues, your catalytic converter is probably fine

If you want to make sure if you have bad O2 or catalytic, get (or borrow) a live data code reader to see the cat and o2 sensor output data. You'll see if they are behaving abnormally.

It could be something as simple as a dirty MAF sensor, dirty o2 sensor or an exhaust leak

 

A live data code reader is different than my OBD II scanner?

 

Reset the code and see if it comes back. Sometimes it will stay off for thousands of miles before showing up again.

Some (maybe most) OBD2 scanners have a function to allow you to see the live data (RPM, throttle position, O2 sensor voltage, fuel trims, coolant & air temperature, etc.) as the engine is running.

 

some OBDII scanners have this function, some don't

I would start with simple things first (clean the MAF sensor and throttle body while you're there) and then clear the code and see if it comes back

 

Live data will chart the numbers while the vehicle is running. Most are upwards of $400 for a good one.

 

@JT1521

This unit is cheap and shows live data. You can download "Torque Engine Management and Diagnostics Tools" software (maybe $20, can't remember ("Torque Lite is free)) for your cellphone and see O2 sensor readouts. I have one and it has performed well on Toyota, Ford, and GM vehicles.

for Android Phones ONLY - Wireless Bluetooth Diagnostic OBD2 Scanner Car Code Reader and Scan Tool for All 1996 & Newer Vehicles ELM327 Compatible OBDII

https://www.amazon.com/gp/product/B005NLQAHS/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

 

Mine was an exhaust leak right before the O2 sensor. Get under there and make sure there isn't a leak before replacing parts

 

For 70 bucks, you can buy a really good code reader made by

SeekOne, got mine on Amazon. It's really,really good. 420 codes can be very deceiving.

 

I agree with accessing the data before replacing parts. The P0420 in my 2000 2.7 was caused by a faulty bank 1 sensor 1 air/fuel rate sensor. The data showed it frozen at one voltage instead of vacillating like it's supposed to.

 

Ok I bought one of these. Will it tell me if one or both O2 sensors is the problem? What exactly am I looking for to see what may be the cause of the P0420 code with this live data diagnostics unit? Thanks.

 

https://www.youtube.com/watch?v=9VZ5K8n5jj0

he explains what data you want to see and what data you do not want to see

 

Ok I am no expert on vehicles. I just ran the Torque Pro app and tested the O2 sensors. Here is the data it shows. Notice no data for the Bank 1 sensor 1. I am either gonna be stupid in saying this or not. lol Does the no data for the Bank 1 Sensor 1 upstream sensor mean its bad or bad wiring and that is the reason for the P0420 code? Here is the data:

 

Anyone know what to make of that?

 

Would be nice to hear anyone's opinion.

 

Before concluding o2 sensor is or cat is bad, have you tried cleaning your MAF sensor and throttle body, or replacing sparkplugs (if it's been a long time since they were last replaced)? Common causes of p0420, with exhaust leaks. Do that, clear the code and see if it comes back

And to answer your question, how long did you let the truck run? To diagnose properly, you need to have the exhaust reach it's normal operating temperature (a few hundred degrees). Sometimes you won't see output data until the sensor or cats have reached operating temperature.

 

I just drove for 15 minutes and then plugged in the BAFX Bluetooth diagnosis plug and it still is not giving me any data for the O2 bank 1 sensor 1. It shows bank 1 sensor 2 data. Can I unplug the bank 1 sensor 1 and check voltage with a digital meter and determine if it's bad? Thanks

 

I see now... if you have a 2000 and later truck, you have an air/fuel sensor (wide-range o2 sensor) as the upstream sensor instead of a regular oxygen sensor. I believe it does show up as the blueish line (o2 sensor 1 wide range voltage).

Usually, upstream sensor readings will fluctuate while downstream sensor will be fairly steady.

yes, you can test oxygen sensors with a voltmeter. The two black wires are the heater element, blue wire is signal + and white is -
https://www.youtube.com/watch?v=DvKZ2GDYEz4

though, if sensor was bad, you would normally get a specific error code for it