Q: P0421 and P0401 codes have appeared

asked by on October 11, 2016

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?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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

My Toyota Sometimes dies when I break or press the gas very slowly

Common causes of engine stalling and rough idle include a faulty mass airflow sensor, faulty engine coolant temperature switch/sensor (typically at cold start only), worn spark plugs, wires or defective ignition coil(s), inadequate fuel delivery or pressure (clogged fuel filter,...

Radio stopped working in my car

It is very hard to tell what could have made the radio quit working and then suddenly work again. However, something that would prevent your radio from working would include: damaged wiring or connectors, something came unplugged, blown fuse, faulty...

Coolant leaks

You may be able to spot the leak by performing a cooling system pressure test. This test is just as it sounds; a special tool is used to apply pressure to the cooling system, making leaks visible. Sometimes however, leaks...

Related articles

P0905 OBD-II Trouble Code: Gate Select Circuit Range/Performance
P0905 means there is an issue within the gate select circuit range/performance often due too the TCM or the select stroke sensor.
P0263 OBD-II Trouble Code: Cylinder Number 1 Contribution/Balance Fault
P0263 P0263 code definition Cylinder Number 1 Contribution/Balance Fault What the P0263 code means P0263 is an [OBD-II diagnostic trouble code] which indicates that the engine control module (ECM) detected the cylinder number 1 having low contribution to the running...
P0221 OBD-II Trouble Code: Throttle/Pedal Position Sensor/Switch B Circuit Range/Performance Problem
P0221 P0221 Code Definition Throttle/Pedal Position Sensor/Switch B Circuit Range/Performance problem What the P0221 code means This code means that the voltage or resistance in the circuitry of the throttle position sensor has fallen out of the acceptable range specified...