Skip the auto shop - Our mechanics make house calls

Q: P0421 comes up on scan. What is the likely culprit

asked by on

What should I need to fix.

My car has 142000 miles.
My car has an automatic transmission.

Hello. When you get the P0421 code, it usually means that you have a failing catalytic converter. It is very common for converters to fail on this vehicle over time. Most of the time I use a scan tool to check the output of the oxygen sensors first, as a bad sensor can cause this code. If the sensors are reading right, then the converter will need to be replaced. If you want to have the code diagnosed, a certified technician from YourMechanic can come to your car’s location to pinpoint the proper repair.

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
  1. Home
  2. Questions
  3. P0421 comes up on scan. What is the likely culprit

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: Will not accelarate over 20mph and has a P0430 code

Hello and thank you for contacting Your Mechanic. The code P0430 means that the catalyst system efficiency is below threshold on bank 2. This is in relation to the catalytic converter not functioning correctly, but this code will not make...

Q: Leaking oil

These engines are known to have oil leaks from multiple gaskets on the engine, power steering leaks, transmission leaks, axle cover leaks, and fill plug leaks. The leaking fluid and location would need to be checked in order to isolate...

Q: Check Engine light on after car won't start

If the car is struggling to start, the battery and starting system need to be checked. A weak battery will not turn the engine over fast enough. Also, there will not be enough power for the fuel pump and ignition....

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
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.