Q: Q: Code p0420

asked by on

Check engine light is on. Got the code p0420. Not sure if it's an o2 sensor, or a catalytic converter?

My car has 146625 miles.
My car has an automatic transmission.

Hello. P0420 could be due to a variety of faults including even a fuel pump that is not supplying sufficient fuel, causing a lean condition, and hence "fooling" the O2 sensors (pre and post) as to the status (i.e., efficiency) of the catalytic converter.

Codes represent "clues" as to where to begin the diagnosis (not necessarily the parts to be replaced) and thus each potential cause associated with the code (and some causes not even listed in the manual) have to be separately diagnosed, that is the individual components have to be tested.

A certified technician, like one from YourMechanic, can evaluate and diagnose the trouble code for you. Be sure to have them check the fuel pump as I recently had a case of this exact code you are inquiring about on a 2001 Pontiac Montana (3.4 L) and it turned out the fuel pump was malfunctioning and the reported code "fault" (i.e., converter efficiency) was simply a consequence, or "artifact" of that fuel pump failure.

Was this answer helpful?
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. Q: Code p0420

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: Misfire and P0420

Hello - the P0420 and the inconsistent waveform for the post-cat O2 sensor might be related to your failing intake manifold gasket issue. If tiny droplets of coolant are being sucked into the engine - one failure mode for this...

Q: Car jerks while driving got a 2006 Ford explorer.

Hi Angel. Thanks for contacting us tonight. Usually, when a car jerks while it's driving or during a shift, it's due to either a fuel/ignition problem with the engine or a restriction of transmission fluid. The coolant leak is likely...

Q: Sway arm broken

Technically, as long as the sway bar doesn't come into contact with other moving parts, or rub on other critical components, you should still be able to operate the vehicle. You will need to understand that the handling will definitely...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
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...
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.