My engine light is on so i took an OBD reading and it showed the error codes P0401, P0420 and P0133. What do I need to fix?

0 2 sensor near the catalytic converter or

replace the catalytic converter

The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar.

Read more at: https://www.obd-codes.com/p0420
Copyright OBD-Codes.com

https://www.obd-codes.com/p0420

P0420-catatytic convertor failure Replace convertor
P0401- EGR flow insufficient-Clean EGR passages
P0730-Faulty transmission shift control-Get diagnosed

The error code p0420 does not rise only due to faulty catalytic converter but may also rise due to one of following reason:

1. Faulty rear O2 sensor

2. Damaged O2 sensor wiring

3. Exhaust leak

The error code p0401 indicates faulty Engine Gas Recirculation (EGR) valve. The remedy to the problem is:

a. Replace EGR valve

b. Repair damaged wiring of EGR valve

c. Clean the EGR valve tubing

Hi there:

DTC P0401 - Insufficient EGR Flow
EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR.

Symptoms
You may notice drivability problems such as pinging (a.k.a. pre-ignition knock) when the engine is under load or the vehicle is at higher speeds. There may also be other symptoms.

A code P0401 most likely means one or more of the following has happened:
The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
There is a blockage in the EGR (tube), most likely carbon buildup
The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum

Possible Solutions:
In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.

Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's & DPFE voltage. There should be a noticable difference in RPM's with the EGR open
Clean out the EGR valve and/or tubing to remove deposits
Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
Replace the DPFE sensor (with a good quality / OEM one)
Replace the EGR valve


DTC P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar.

This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms: The main symptom to the driver is the illumination of the MIL (malfunction indicator lamp). You will likely not notice any drivability problems, although there may be symptoms. For example, if the substance inside the catalytic converter is broken or failed, it may be restricting the exhaust which will result in a feeling of reduced power output from the vehicle.

A code P0420 may mean that one or more of the following has happened:
Leaded fuel was used where unleaded was called for
A damaged or failed oxygen sensor (HO2S)
Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
The engine coolant temperature sensor is not working properly
Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
******** spark timing
The oxygen sensors in front and behind the converter are reporting too similar of readings
Leaking fuel injector or high fuel pressure
Cylinder misfire
Oil contamination

Possible Solutions: Some suggested steps for troubleshooting a P0420 error code include:
Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
Inspect the downstream heated oxygen sensor (HO2S), replace if necessary
Replace the catalytic converter

Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.

We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.


Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

For OBD code problems check the list of help links below. Click the link below to go through its procedure.--------------Diagnostic Code P2195?http://schematicsdiagram.blogspot.in/2012/02/diagnostic-code-p2195-on-toyota-avalon.html--------------Diagnostic code P1330?http://technoanswers.blogspot.in/2012/02/diagnostic-code-p1330-on-kia-2wd.html------------Diagnostic code P0700, P1330, P1121?http://technoanswers.blogspot.in/2012/02/diagnostic-code-p0700-p1330-p1121-on.html-------------shows error code P1330?http://technoanswers.blogspot.in/2012/02/2003-kia-sorento-shows-error-code-p1330.html--------OBD code P1330?http://technoanswers.blogspot.in/2012/02/obd-code-p1330-on-2003-kia-sorento.html------------OBD code P01300?http://technoanswers.blogspot.in/2012/02/obd-code-p01300-on-toyota-rav4.html--------------OBD code P0768?http://repairhelpcenter.blogspot.com/2012/01/obd-code-p0768.html------------Evaporative Emissions System codes details?http://schematicsdiagram.blogspot.com/2011/11/evaporative-emissions-system-codes.html--------------- Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

----------------

Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

--------------
ABS trouble codes for all models?

http://repairhelpcenter.blogspot.com/2011/11/abs-trouble-codes-for-all-1994-00-acura.html

------------
Diagnostic code P0010?http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-p0010.html-------------Diagnostic Code P1396?

http://howtobyme.blogspot.com/2011/11/diagnostic-code-p1396.html

--------------
Code P0452?

http://howtobyme.blogspot.com/2011/11/code-p0452.html

-------------

OBD code P0172 on Buick?

http://howtobyme.blogspot.com/2011/11/obd-code-p0172-on-buick-park-avenue.html

-------------
DTC Code P0321?

http://howtobyme.blogspot.com/2011/11/dtc-code-p0321-on-buick-park-avenue.html

------------------

Error Code P0471?

http://howtobyme.blogspot.com/2011/11/error-code-p0471-on-2007-dodge-ram-3500.html

-------------
P0304 Error code?

http://howtobyme.blogspot.com/2011/11/p0304-error-code-on-dodge-neon.html

-----------------

OBDII scan is receiving NO BUS CODE?

http://howtobyme.blogspot.com/2011/11/obdii-scan-is-receiving-no-bus-code.html

-----------
How to Clear OBD error Codes?

http://repairhelpcenter.blogspot.com/2011/11/how-to-clear-obd-error-codes-on-acura.html

----------------
Diagnosis and Testing Car Components?

http://vwrepairhelp.blogspot.com/2011/11/diagnosis-and-testing-car-components.html

--------------
Diagnostic Trouble Codes list?

Part 1.

http://repairhelpcenter.blogspot.com/2011/11/diagnostic-trouble-codes-list-for-acura_18.html

--------------
Diagnostic Trouble Codes list?

Part 2.------

http://repairhelpcenter.blogspot.com/2011/11/diagnostic-trouble-codes-list-for-acura.html

------------
OBD Code is cleared but check engine light will not RESET?

http://schematicsdiagram.blogspot.in/2012/02/obd-code-is-cleared-but-check-engine.html

--------------
Diagnostic Code 43 and 71?

http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-43-and-71-on-1991.html

------------------
Code P0132?

http://schematicsdiagram.blogspot.com/2011/12/code-p0132-on-acura-tl.html

-------------
P0031 code?

http://schematicsdiagram.blogspot.com/2011/12/p0031-code-on-dodge-dakota.html

--------------
How to get diagnostic Code without OBD Scanner on Pre 1995 cars?

http://schematicsdiagram.blogspot.com/2011/12/how-to-get-diagnostic-code-without-obd.html

------------
OBD-II Trouble Code P0300?

http://schematicsdiagram.blogspot.com/2011/12/obd-ii-trouble-code-p0300.html

-------------
Getting diagnostic code P0016?

http://schematicsdiagram.blogspot.com/2011/12/getting-diagnostic-code-p0016.html

--------------
How to Read Codes from Check Engine Light?

http://schematicsdiagram.blogspot.com/2011/12/how-to-read-codes-from-check-engine.html

-------------
Diagnostic Code P0540 continues to return and the MIL light is on?

http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-p0540-continue-to.html

-----------
DTC Trouble Code P0401?

http://schematicsdiagram.blogspot.com/2012/01/dtc-trouble-code-p0401.html

-----------------
Car misfires and error code P0306 and P0303 is shown?

http://technoanswers.blogspot.com/2012/01/car-misfires-and-error-code-p0306-and.html

-------------
Diagnostic code P0463?

http://technoanswers.blogspot.com/2012/01/diagnostic-code-p0463-on-ford-f250.html

-------------
Check engine light with codes P2195 and P2197?

http://howtobyme.blogspot.in/2012/01/check-engine-light-with-codes-p2195-and.html

------------
Diagnostic error code P0121,P0505,P1000,P2101,P2104, P2110,P2135,P2106?

http://technoanswers.blogspot.in/2012/01/diagnostic-error-code.html

--------------
P0174, P0037 and P2197?

http://technoanswers.blogspot.in/2012/02/p0174-p0037-and-p2197-on-toyota-rav4.html

-----------
P0352 Obd code?

http://technoanswers.blogspot.in/2012/02/p0352-obd-code-on-toyota-rav4.html

-------------
Error code p0402?

http://technoanswers.blogspot.in/2012/02/error-code-p0402-on-ford-escape.html

---------
Obd Code P0763?

http://technoanswers.blogspot.in/2012/02/obd-code-p0763-on-lexus.html

-------
OBD code P0301, P0430 and P0174?

http://schematicsdiagram.blogspot.in/2012/02/obd-code-p0301p0430-and-p0174.html

---------
OBD code P0500?http://schematicsdiagram.blogspot.in/2012/02/obd-code-p0500-on-lexus-rx-300.html
-----------This will help.Thanks.

For OBD code problems check the list of help links below. Click the link below to go through its procedure.

--------------
Diagnostic Code P2195? http://schematicsdiagram.blogspot.in/2012/02/diagnostic-code-p2195-on-toyota-avalon.html

--------------
Diagnostic code P1330? http://technoanswers.blogspot.in/2012/02/diagnostic-code-p1330-on-kia-2wd.html

------------
Diagnostic code P0700, P1330, P1121? http://technoanswers.blogspot.in/2012/02/diagnostic-code-p0700-p1330-p1121-on.html

-------------
shows error code P1330? http://technoanswers.blogspot.in/2012/02/2003-kia-sorento-shows-error-code-p1330.html

--------
OBD code P1330? http://technoanswers.blogspot.in/2012/02/obd-code-p1330-on-2003-kia-sorento.html

------------
OBD code P01300? http://technoanswers.blogspot.in/2012/02/obd-code-p01300-on-toyota-rav4.html

--------------
OBD code P0768? http://repairhelpcenter.blogspot.com/2012/01/obd-code-p0768.html

------------
Evaporative Emissions System codes details? http://schematicsdiagram.blogspot.com/2011/11/evaporative-emissions-system-codes.html --------------- Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

----------------

Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

--------------
ABS trouble codes for all models?

http://repairhelpcenter.blogspot.com/2011/11/abs-trouble-codes-for-all-1994-00-acura.html

------------
Diagnostic code P0010? http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-p0010.html

-------------
Diagnostic Code P1396?

http://howtobyme.blogspot.com/2011/11/diagnostic-code-p1396.html

--------------
Code P0452?

http://howtobyme.blogspot.com/2011/11/code-p0452.html

-------------

OBD code P0172 on Buick?

http://howtobyme.blogspot.com/2011/11/obd-code-p0172-on-buick-park-avenue.html

-------------
DTC Code P0321?

http://howtobyme.blogspot.com/2011/11/dtc-code-p0321-on-buick-park-avenue.html

------------------

Error Code P0471?

http://howtobyme.blogspot.com/2011/11/error-code-p0471-on-2007-dodge-ram-3500.html

-------------
P0304 Error code?

http://howtobyme.blogspot.com/2011/11/p0304-error-code-on-dodge-neon.html

-----------------

OBDII scan is receiving NO BUS CODE?

http://howtobyme.blogspot.com/2011/11/obdii-scan-is-receiving-no-bus-code.html

-----------
How to Clear OBD error Codes?

http://repairhelpcenter.blogspot.com/2011/11/how-to-clear-obd-error-codes-on-acura.html

----------------
Diagnosis and Testing Car Components?

http://vwrepairhelp.blogspot.com/2011/11/diagnosis-and-testing-car-components.html

--------------
Diagnostic Trouble Codes list?

Part 1.

http://repairhelpcenter.blogspot.com/2011/11/diagnostic-trouble-codes-list-for-acura_18.html

--------------
Diagnostic Trouble Codes list?

Part 2.------

http://repairhelpcenter.blogspot.com/2011/11/diagnostic-trouble-codes-list-for-acura.html

------------
OBD Code is cleared but check engine light will not RESET?

http://schematicsdiagram.blogspot.in/2012/02/obd-code-is-cleared-but-check-engine.html

--------------
Diagnostic Code 43 and 71?

http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-43-and-71-on-1991.html

------------------
Code P0132?

http://schematicsdiagram.blogspot.com/2011/12/code-p0132-on-acura-tl.html

-------------
P0031 code?

http://schematicsdiagram.blogspot.com/2011/12/p0031-code-on-dodge-dakota.html

--------------
How to get diagnostic Code without OBD Scanner on Pre 1995 cars?

http://schematicsdiagram.blogspot.com/2011/12/how-to-get-diagnostic-code-without-obd.html

------------
OBD-II Trouble Code P0300?

http://schematicsdiagram.blogspot.com/2011/12/obd-ii-trouble-code-p0300.html

-------------
Getting diagnostic code P0016?

http://schematicsdiagram.blogspot.com/2011/12/getting-diagnostic-code-p0016.html

--------------
How to Read Codes from Check Engine Light?

http://schematicsdiagram.blogspot.com/2011/12/how-to-read-codes-from-check-engine.html

-------------
Diagnostic Code P0540 continues to return and the MIL light is on?

http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-p0540-continue-to.html

-----------
DTC Trouble Code P0401?

http://schematicsdiagram.blogspot.com/2012/01/dtc-trouble-code-p0401.html

-----------------
Car misfires and error code P0306 and P0303 is shown?

http://technoanswers.blogspot.com/2012/01/car-misfires-and-error-code-p0306-and.html

-------------
Diagnostic code P0463?

http://technoanswers.blogspot.com/2012/01/diagnostic-code-p0463-on-ford-f250.html

-------------
Check engine light with codes P2195 and P2197?

http://howtobyme.blogspot.in/2012/01/check-engine-light-with-codes-p2195-and.html

------------
Diagnostic error code P0121,P0505,P1000,P2101,P2104, P2110,P2135,P2106?

http://technoanswers.blogspot.in/2012/01/diagnostic-error-code.html

--------------
P0174, P0037 and P2197?

http://technoanswers.blogspot.in/2012/02/p0174-p0037-and-p2197-on-toyota-rav4.html

-----------
P0352 Obd code?

http://technoanswers.blogspot.in/2012/02/p0352-obd-code-on-toyota-rav4.html

-------------
Error code p0402?

http://technoanswers.blogspot.in/2012/02/error-code-p0402-on-ford-escape.html

---------
Obd Code P0763?

http://technoanswers.blogspot.in/2012/02/obd-code-p0763-on-lexus.html

-------
OBD code P0301, P0430 and P0174?

http://schematicsdiagram.blogspot.in/2012/02/obd-code-p0301p0430-and-p0174.html

---------
OBD code P0500?

http://schematicsdiagram.blogspot.in/2012/02/obd-code-p0500-on-lexus-rx-300.html

-----------

This will help.

Thanks.

------------------------------------

For OBD code problems check the list of help links below. Click the link below to go through its procedure.--------------Diagnostic Code P2195?http://schematicsdiagram.blogspot.in/2012/02/diagnostic-code-p2195-on-toyota-avalon.html--------------Diagnostic code P1330?http://technoanswers.blogspot.in/2012/02/diagnostic-code-p1330-on-kia-2wd.html------------Diagnostic code P0700, P1330, P1121?http://technoanswers.blogspot.in/2012/02/diagnostic-code-p0700-p1330-p1121-on.html-------------shows error code P1330?http://technoanswers.blogspot.in/2012/02/2003-kia-sorento-shows-error-code-p1330.html--------OBD code P1330?http://technoanswers.blogspot.in/2012/02/obd-code-p1330-on-2003-kia-sorento.html------------OBD code P01300?http://technoanswers.blogspot.in/2012/02/obd-code-p01300-on-toyota-rav4.html--------------OBD code P0768?http://repairhelpcenter.blogspot.com/2012/01/obd-code-p0768.html------------Evaporative Emissions System codes details?http://schematicsdiagram.blogspot.com/2011/11/evaporative-emissions-system-codes.html--------------- Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

----------------

Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

--------------
ABS trouble codes for all models?

http://repairhelpcenter.blogspot.com/2011/11/abs-trouble-codes-for-all-1994-00-acura.html

------------
Diagnostic code P0010?http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-p0010.html-------------Diagnostic Code P1396?

http://howtobyme.blogspot.com/2011/11/diagnostic-code-p1396.html

--------------
Code P0452?

http://howtobyme.blogspot.com/2011/11/code-p0452.html

-------------

OBD code P0172 on Buick?

http://howtobyme.blogspot.com/2011/11/obd-code-p0172-on-buick-park-avenue.html

-------------
DTC Code P0321?

http://howtobyme.blogspot.com/2011/11/dtc-code-p0321-on-buick-park-avenue.html

------------------

Error Code P0471?

http://howtobyme.blogspot.com/2011/11/error-code-p0471-on-2007-dodge-ram-3500.html

-------------
P0304 Error code?

http://howtobyme.blogspot.com/2011/11/p0304-error-code-on-dodge-neon.html

-----------------

OBDII scan is receiving NO BUS CODE?

http://howtobyme.blogspot.com/2011/11/obdii-scan-is-receiving-no-bus-code.html

-----------
How to Clear OBD error Codes?

http://repairhelpcenter.blogspot.com/2011/11/how-to-clear-obd-error-codes-on-acura.html

----------------
Diagnosis and Testing Car Components?

http://vwrepairhelp.blogspot.com/2011/11/diagnosis-and-testing-car-components.html

--------------
Diagnostic Trouble Codes list?

Part 1.

http://repairhelpcenter.blogspot.com/2011/11/diagnostic-trouble-codes-list-for-acura_18.html

--------------
Diagnostic Trouble Codes list?

Part 2.------

http://repairhelpcenter.blogspot.com/2011/11/diagnostic-trouble-codes-list-for-acura.html

------------
OBD Code is cleared but check engine light will not RESET?

http://schematicsdiagram.blogspot.in/2012/02/obd-code-is-cleared-but-check-engine.html

--------------
Diagnostic Code 43 and 71?

http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-43-and-71-on-1991.html

------------------
Code P0132?

http://schematicsdiagram.blogspot.com/2011/12/code-p0132-on-acura-tl.html

-------------
P0031 code?

http://schematicsdiagram.blogspot.com/2011/12/p0031-code-on-dodge-dakota.html

--------------
How to get diagnostic Code without OBD Scanner on Pre 1995 cars?

http://schematicsdiagram.blogspot.com/2011/12/how-to-get-diagnostic-code-without-obd.html

------------
OBD-II Trouble Code P0300?

http://schematicsdiagram.blogspot.com/2011/12/obd-ii-trouble-code-p0300.html

-------------
Getting diagnostic code P0016?

http://schematicsdiagram.blogspot.com/2011/12/getting-diagnostic-code-p0016.html

--------------
How to Read Codes from Check Engine Light?

http://schematicsdiagram.blogspot.com/2011/12/how-to-read-codes-from-check-engine.html

-------------
Diagnostic Code P0540 continues to return and the MIL light is on?

http://schematicsdiagram.blogspot.com/2011/12/diagnostic-code-p0540-continue-to.html

-----------
DTC Trouble Code P0401?

http://schematicsdiagram.blogspot.com/2012/01/dtc-trouble-code-p0401.html

-----------------
Car misfires and error code P0306 and P0303 is shown?

http://technoanswers.blogspot.com/2012/01/car-misfires-and-error-code-p0306-and.html

-------------
Diagnostic code P0463?

http://technoanswers.blogspot.com/2012/01/diagnostic-code-p0463-on-ford-f250.html

-------------
Check engine light with codes P2195 and P2197?

http://howtobyme.blogspot.in/2012/01/check-engine-light-with-codes-p2195-and.html

------------
Diagnostic error code P0121,P0505,P1000,P2101,P2104, P2110,P2135,P2106?

http://technoanswers.blogspot.in/2012/01/diagnostic-error-code.html

--------------
P0174, P0037 and P2197?

http://technoanswers.blogspot.in/2012/02/p0174-p0037-and-p2197-on-toyota-rav4.html

-----------
P0352 Obd code?

http://technoanswers.blogspot.in/2012/02/p0352-obd-code-on-toyota-rav4.html

-------------
Error code p0402?

http://technoanswers.blogspot.in/2012/02/error-code-p0402-on-ford-escape.html

---------
Obd Code P0763?

http://technoanswers.blogspot.in/2012/02/obd-code-p0763-on-lexus.html

-------
OBD code P0301, P0430 and P0174?

http://schematicsdiagram.blogspot.in/2012/02/obd-code-p0301p0430-and-p0174.html

---------
OBD code P0500?http://schematicsdiagram.blogspot.in/2012/02/obd-code-p0500-on-lexus-rx-300.html
-----------This will help.Thanks.

This error means Exhaust Gas Recirculation Flow Insufficient Detected.

You can deatils on the following site http://www.permoveo.ltd.uk/tabid/122/OBD-Error-Code/P0401/Diagnostics/Hyundai/Default.aspx

but for convenience I have reproduced that information here:
.
Generic OBD Error Code Details for P0401 Exhaust Gas Recirculation Flow Insufficient Detected What does this mean? OBD Code P0401refers to
EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR. SymptomsPossible sumptoms of OBD code P0401
You may notice drivability problems such as pinging (a.k.a. pre-ignition knock) when the engine is under load or the vehicle is at higher speeds. There may also be other symptoms. CausesPossible causes of OBD code P0401
A code P0401 most likely means one or more of the following has happened: •The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced•There is a blockage in the EGR (tube), most likely carbon buildup •The EGR valve is faulty •The EGR valve may not be opening due to a lack of vaccuum Possible SolutionsIn fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit. •Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's & DPFE voltage. There should be a noticable difference in RPM's with the EGR open •Clean out the EGR valve and/or tubing to remove deposits•Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)•Replace the DPFE sensor (with a good quality / OEM one)•Replace the EGR valve Related CodesP0400 P0402 P0403

Causes A code P0420 may mean that one or more of the following has happened:

• Leaded fuel was used where unleaded was called for
• An oxygen sensor is not reading (functioning) properly
• The engine coolant temperature sensor is not working properly
• Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
• Retarded spark timing
• The oxygen sensors in front and behind the converter are reporting too similar of readings

Robert

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Based on what the tech manuals say I would change the DPFE sensor for the EGR Valve, careful not to tear the special silicone rubber hoses that go to it from the exhaust, as a Ford dealer tech I saw these codes allot, and the DPFE sensor was almost always the issue or the hoses going to it.