Skip the auto shop - Our mechanics make house calls

Q: P0421 and P0401 codes have appeared

asked by on

I took my car to get it diagnosed and the codes p0421 and p0401 popped up... can I know what is... is it something to be concerned? And which one should I take care of first... they told me that it'll come out to 700.00 to get it repaired

My car has 219000 miles.
My car has an automatic transmission.

Hello. The codes P0421 and P0401 refer to the oxygen sensor and EGR valve, respectively. It is possible that an issue with one is causing the fault to be seen by the other, as they will work loosely together. It would be best to have a certified technician perform diagnostics on the codes to pinpoint the problem. They can hook a scanner up to the vehicle and read the actual data from the components, and this will show them where they will need to look for the fault.

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: I have a Mitsubishi Lancer LS 2002 it has a new clutch pressure plate and throwout bearing I bled the clutch 5 times I driver for

It could be that you have a leak in the clutch master or slave cylinder. Either one can cause the clutch to lose pressure that way. Unfortunately, The 02 Lancers had a "concentric" slave cylinder that requires transmission removal for...

Q: I plan on putting a 6g74 from a Diamante

Hey there. The 6G74 is a direct drop in as long as the donor vehicle is the right one. That engine was used in a few models with some being FWD and others AWD, and there will be very subtle...

Q: Tengo una hyundai santa fe el código que me dice es p0421 q pieza puede ser ? Por el muffle huele raro

Hello, thank you for writing in. The code P0421 means the exhaust system is detecting an issue with the fumes being to rich. This can happen when the spark plugs are worn and cause the fuel not to burn correctly,...

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...
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.