Skip the auto shop - Our mechanics make house calls

Q: Diagnosed as code P0420

asked by on

The Engine light came on. I went to the mechanic an it was diagnosed as a code P0420.

A: When you get a P0420 code that indicates a ...

When you get a P0420 code that indicates a failing catalytic converter. Most of the time that is exactly what it is. In some cases, it can also be caused by a bad oxygen sensor. I typically use a computer scan tool to monitor the signal coming from the oxygen sensors. If they are not reading correctly then they need to be replaced. If they are fine then the catalytic converter needs to be replaced. If you would like to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to make a diagnosis and to replace either your oxygen sensor or catalytic converter.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: No heat or cool with the remote start.

Hi there. You could have the power wires with the heating and air conditioning system connected to the remote switch to allow them to come on when the vehicle is started. If the system is not allowing you to have...

Q: P0231 code coming on - reduced RPM and trembling with the AC on

Diagnostic Trouble Code P0231 relates to a problem with the wiring in the fuel pump circuit, although it is also possible to have a faulty fuel pump that draws too much current and creates a voltage drop in the circuit....

Q: Cold air doesn't come out of the vent

Hi there, thanks for writing in. If you are only getting ambient air temperature out of the vents, then your compressor is not on. You may need to have the A/C checked to see if refrigerant has leaked out or...

Related articles

How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.