What does P0420 code mean ?

P0420 means that Catalyst system efficiency below threshold (Bank 1). P in the p0420 abbreviation of "Powertrain". This group of OBD/2 codes is related in engine troubles. P0420 is an inefficient catalytic convertor code.

If your vehicle mileage is less than 50K miles, catalytic converters typically don't just go bad at that many miles. There is likely something else going on. Often it is an injector dumping or leaking excess gas into the engine. Or the dealer could have used some sort of cleaner that damaged it. You really need to know exactly what these shops are doing because modern vehicles are not very tolerant of some old school "tune up" methods. The fact that it happened after they worked on it seems unlikely to be a coincidence.

How to diagnose P0420 ?

The fixing of the P0420 code of your depends on its cause. First, check the reason behind the code and then fix it accordingly.

Following these can almost always fix the P0420 code.

What causes a P0420 code in ?

A bad cat (common) or O2 sensor(s) are the most likely causes P0420, followed by an exhaust leak between the header and cat (flex pipe).

Or being a vacuum leak causes P0420.

Or the vehicle may be having some type of spark knock.

Also check the flex pipe between the exhaust and the catalytic converter for leaks/damage. The exhaust flex pipe in the Sonic takes a lot of abuse being so near the roadway/ground and rust apart causing the sensors throw this P0420 code.

Or check the list please :
Check other possible p0420 causes with the descriptions:

If the main reason is bad cat , these reasons can cause it : bad AFM cylinder, leaky injector or low octane gas.

P0420 Symptoms :

Check engine light shows an engine error, when you diagnose it with obd scanner you can see p0420 code, so the first symptom is catalytic converter not working properly.

Another symptom is ECU is not pulling any timing or fuel to manage the poor catalyst efficiency.

How to fix P0420 code ?

Check O2 sensors are oscillating between 0.200 and 0.800 volts if it is fine the problem is in cat. converter.

Another advice : Replace battery cables, buy a new fuse bus and greased all connections, cranked the car and the code immediately will disappear.

Easy way to do is replacing the catalytic convertor with the new one. Yes it can be expensive but for your vehicle health and engine condition to prevent other fault codes it will be the best way.

Common Mistakes P0420 Fixing Procedure :

- O2 sensors MUST be OEM (and must be the correct part numbers: there are two different upstream/bank 1 O2 sensors for these engines and I believe they both fit. Use your VIN when ordering).

-Vacuum system MUST be completely sealed.

-Check your flex pipe with a flashlight. It can be easy to mis small cracks/tears.

-Who is resetting your codes and how are they doing it? They need to be able to read live data with a scan tool. There is no other way to perform a complete test of the electronics that are impacting that code. In other words, a code reader is not sufficient.

-The factory service manual of states that your code may still return for approximately the first 100 miles because the new materials are off-gassing/breaking in as they heat cycle for the first few times. Don't panic if the code comes on after a new catalytic converter. Drive it for 100 miles, reset the code, and see if it comes back.

How much does it cost to fix a P0420 code ?

P0420 code is a worn catalytic converter can cost over $1000 for .But if the problem is in the o2 sensors this will be cheaper than cat. converter.

Please don't forget you will pay also service fee for the replacement parts.

Will P0420 code clear itself ?

After fixing/replacing o2 sensors or catalytic converter %99 it will clear itself automaticly.

Common Questions & Answers About P0420 Code

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