Skip the auto shop - Our mechanics make house calls

Q: The engine light is on and the code is P0420 - Catalyst System Efficiency Below Threshold Bank . What part do I need to fix it?

asked by on

The engine light is on and we just want to know what the part needed to fix this issue. the code is P0420 - Catalyst System Efficiency Below Threshold Bank . However I dont know if its downstream or upstream.

My car has 130267 miles.
My car has an automatic transmission.

While a number of things like a faulty oxygen sensor or exhaust leak can cause fault code P0420 to be set, the most common fault is the catalytic converter itself. However, as a replacement can be very expensive, your best be is to have a certified technician properly diagnose why code P0420 was set in the system.

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!
  1. Home
  2. Questions
  3. The engine light is on and the code is P0420 - Catalyst System Efficiency Below Threshold Bank . What part do I need to fix it?

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: I have a problem with jeep running rough about once every seven or eight days

Hello. This may suggest a problem with the ECU resetting codes that otherwise would remain there. When the ECU detects a problem with the engine or any other operation, it will cause the check engine light to come on and...

Q: What does it cost to repair/replace the electronic power steering

There are many different parts to the electronic power steering on your 2011 Hyundai Elantra. I cannot provide a quote without knowing more about what is causing the EPS light. Common failures are steering angle sensors, the power steering rack,...

Q: No reverse light or horn - 1982 Chevrolet C30

Check the reverse light switch (located on the transmission?) to be sure it is closing the circuit when Reverse is selected. Make sure there is power to the switch, throught the switch, then power to the reverse light bulbs. 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...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
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.