Q: Q: Code p0421

asked by on

I am getting a p0421 code but I just replaced the catalytic converter. I got the code erased after but it popped back on. My car seems to stumble/put a lot though. What else could it be?

My car has 148000 miles.
My car has an automatic transmission.

Most mechanics will use a diagnostic scan tool to download the source of the error codes. In the case of the P-0421, we usually find that either the catalytic converter has run its course, or the O2 sensors are giving faulty data and need to be replaced at the same time. If you’d like, a certified YourMechanic technician can come to your location to help you diagnose this code or replace the O2 sensors in your vehicle. To be safe, we recommend replacing all of the O2 sensors.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 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!
  1. Home
  2. Questions
  3. Q: Code p0421

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: Surging idle

Hello, I would start with checking things like the idle control valve and looking for vacuum leaks. Additional things to check might be an EGR valve that may be stuck open or clogged EGR ports, an intermittent or faulty connection...

Q: Car always starts but sometimes won't stay running

Claimed by Jeff Engstrom

Q: Car shakes when I'm idel. What could be wrong and how much to fix it?

Based on your symptoms of rough idle and a check engine light, I would recommend a check engine light inspection. This will help to determine the exact cause of the rough running and check engine light. Consider YourMechanic as check...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.
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.