Question about 1996 Toyota Corolla

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What are the probable causes of DTC P0401?

Already had fuel EGR passes cleaned and replaced vacuum solenoid..check engine light back

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  • Toyota Master
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Faulty egr valve might need a new one

Posted on May 02, 2015

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It shows code P0401. Already replaced the EGR valve and catalytic converter plus sensors. What now.


You didn't say if you have any symptoms so I will assume you don't. After you made the repairs, you have to have the code removed. Any major auto parts store will do it for free. If the code don't come back, its fixed.

Mar 23, 2015 | 2001 Hyundai Santa Fe

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P0401


if you feel ok with it take off the air intake and remove the throttle body to check for any carbine build up. the cause for this code is that the flow for the exhaust is insufficient. also it could be the cad. convertor. you could disconnect the catalectic convertor to see if the code stays gone but I would check for build up first if you do not feel like you can do this see an expert. good luck

Apr 11, 2014 | 2001 Mitsubishi Montero Sport 4WD

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Have 1999 Mercury Sable and failed emissions for P0401 code, I replaced the EGR Valve and had the code reset, service engine light came on again Approx 15 miles later. Took it to Auto Zone and they gave...


I am not surprized. The chances that replacing an EGR valve will fix a code P0401 on ANY Ford vehicle is about 1/2 of 1 percent. You most likely either have clogged up EGR ports in your intake manifold, or you have a defective Delta Pressure Feedback EGR (DPFE) sensor.

To find out which it is, apply vacuum to the EGR valve vacuum port with the engine idling. The engine should stumble and/or stall. If it does not, your ports are clogged. If it does, the most likely cause of your problem is the DPFE sensor. However, the EGR vacuum control solenoid could also be the cause.
You cannot properly test the EGR vacuum control solenoid without the proper equipment, but you can check to make sure that there is manifold vacuum going into one side of the solenoid and you can check to make sure that there are no breaks or leaks in the line that runs between the solenoid and the valve. If you find any of these, repair as necessary. If you do not find a problem with the vacuum lines, then you can take a "guess" and replace the DPFE. If this does not work, then you can "guess" again and replace the solenoid. If it still does nort work, then you probably have a bad electrical circuit to the solenoid (once again, requiring the proper equipment to diagnose).

Please also review the following article: What Else Could Be Wrong?

Nov 18, 2011 | 1999 Mercury Sable

1 Answer

I just replaced the egr valve in my 1997 dodge caravan 2 days ago. The service engine light came back on, and I got the same p0401 code. What should I look for now?


it may help to tell what engine you have. P0401 doesnt mean the egr valve was bad, it means the egr isnt opening for some reason OR not flowing. Egr valves rarely are "bad" check if all vacuum lines are connected and clear. the egr vacuum solenoid is famous for being bad. als make sure the passage from the egr valve to the intake manifold is clean and flowing. Its like flushing a toilet thats clogged.. All the valves are working, but its not flowing.

Aug 03, 2011 | Dodge Caravan Cars & Trucks

1 Answer

I have a 98 ford escort check engine said p0401 what do that mean


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.

Causes: 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

Check and test it; hope helps.

Mar 18, 2011 | Ford Escort Cars & Trucks

1 Answer

Check engine light stays on the code that keeps coming up is P0401 changed egr valve clened out carbon build up also smell gas when first start not driving and fuel millage not as good car runs good though...


Could be a EGR vacuum issue or temp sensor issue

Common Problems That Trigger the P0401 Code
  • Restriction in the EGR passages, usually caused by carbon buildup
  • Lack of a proper vacuum signal to the EGR Valve from EGR Vacuum Solenoid
  • EGR Vacuum Modulator is defective
  • EGR Temperature Sensor is defective
  • EGR Valve is defective
This is from:
http://repairpal.com/OBD-II-Code-P0401-Ford

Jan 31, 2011 | 1998 Chevrolet Lumina

1 Answer

I have problem in chevy silverado model 2008 trouble cods p0101-p0401 can any body help???


P0101 - Mass Air Flow (MAF) Circuit Range/Performance Problem
Basically this means that there is a problem with the Mass Air Flow (MAF) sensor or circuit. The PCM detects that the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value for more than 4.0 seconds. Other MAF sensor circuit DTC trouble codes are P0100, P0102, P0103, and P0104.

Symptoms: You will likely not notice any serious drivability problems, although there may be symptoms.

Possible Solutions: The simplest thing to do is to reset the code and see if it comes back. Then start with the cheapest, easiest repair procedures:
* Inspect for the following conditions:
An incorrectly routed harness--Inspect the harness of the MAF sensor in order to verify that it is not routed too close to the following components:
- The secondary ignition wires or coils
- Any solenoids
- Any relays
- Any motors
* A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor.
* A wide open throttle (WOT) acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 6-12 g/s at idle to 230 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
* The barometric pressure (BARO) that is used in order to calculate the predicted MAF value is initially based on the MAP sensor at key ON.
* When the engine is running the MAP sensor value is continually updated near WOT. A skewed MAP sensor will cause the calculated MAF value to be inaccurate. The value shown for the MAP sensor display varies with the altitude. With the ignition ON and the engine OFF, 103 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 feet) of altitude.
* A high resistance on the ground circuit of the MAP sensor can cause this DTC to set.
* Any loss of vacuum to the MAP sensor can cause this DTC to set.

If you suspect the condition may be related to aftermarket accessories, refer to Checking Aftermarket Accessories in Wiring Systems.

Check this it is here as an aid in resolving your P0101 trouble code (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.

Causes: 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


Keep us updated.

Jan 11, 2011 | 2008 Chevrolet Silverado 3500HD 2WD

1 Answer

2002 Mercury cugar P0401 and P1401


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.

Causes: 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 P1401 - Differential Pressure Feedback Electronic Sensor circuit High Voltage

I think that you need a new DPFE; first check it, you could also have something restricted. There are ports in the throttle body that can cause this as well. Check THIS LINK.

Hope helps.

Nov 04, 2010 | Mercury Cougar Cars & Trucks

2 Answers

Check engine light comes on and off, auto zone test read back EGR flow insufficient/manufact.specif.DTC/see service manual.what does any of that mean?HONDA ACCORD 4CYL.2001


The EGR valve helps your car more efficiently and completely burn fuel by recirculating a portion of your exhaust and running it through the combustion process again. When the EGR valve goes bad, it must be replaced.

The EGR valve, or Exhaust Gas Recirculation valve, is a vacuum controlled valve which allows a specific amount of your exhaust back into the intake manifold. This exhaust mixes with the intake air and actually cools the combustion process. Cooler is always better inside your engine. The exhaust your EGR valve recirculates also prevents the formation of Nitrogen related gases. These are referred to as NOX emissions, and are a common cause for failing emissions testing. Unfortunately, your EGR valve can get stuck, causing NOX gases to build up. You'll know if your EGR valve is stuck or malfunctioning because your car will experience symptoms like rough idle and bucking on acceleration.

Here is a picture of where the EGR Valve is located (Accord 1999). Replacing it is fairly simple and straightforward. A vacuum line and a couple of bolts. You'll see what you have to do when you look at it.

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If you are replacing the EGR Valve due to the Check Engine Light (MIL) being on with a DTC P0401 then I suggest contacting your Honda Dealer. There was a Product Update Campaign (PUD) in the fall of 1999 that corrected the problem.

Another times, the clean is the solution...I hope help yoiu with this. Good luck, and remember rated this help.

Sep 03, 2009 | 2001 Honda Accord

1 Answer

Egr vacuum solenoid


Exhaust Gas Recirculation (EGR) System Monitor—Differential Pressure Feedback EGR The Differential Pressure Feedback EGR System Monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Input from the ECT, CHT, IAT, TP and CKP sensors is required to activate the EGR System Monitor. Once activated, the EGR System Monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR System Monitor tests are also performed during on demand self-test.
  1. The differential pressure feedback EGR sensor and circuit are continuously tested for opens and shorts. The monitor looks for the Differential Pressure Feedback EGR circuit voltage to exceed the maximum or minimum allowable limits.

    The DTCs associated with this test are DTCs P1400 and P1401.
  1. The EGR vacuum regulator solenoid is continuously tested for opens and shorts. The monitor looks for an EGR Vacuum Regulator circuit voltage that is inconsistent with the EGR Vacuum Regulator circuit commanded output state.

    The DTC associated with this test is DTC P1409.
  1. The test for a stuck open EGR valve or EGR flow at idle is continuously performed whenever at idle (TP sensor indicating closed throttle). The monitor compares the Differential Pressure Feedback EGR circuit voltage at idle to the Differential Pressure Feedback EGR circuit voltage stored during key on engine off to determine if EGR flow is present at idle.

    The DTC associated with this test is DTC P0402.
  1. The differential pressure feedback EGR sensor upstream hose is tested once per drive cycle for disconnect and plugging. The test is performed with EGR valve closed and during a period of acceleration. The PCM will momentarily command the EGR valve closed. The monitor looks for the differential pressure feedback EGR sensor voltage to be inconsistent for a no flow voltage. A voltage increase or decrease during acceleration while the EGR valve is closed may indicate a fault with the signal hose during this test.

    The DTC associated with this test is DTC P1405.
  1. The EGR flow rate test is performed during a steady state when engine speed and load are moderate and EGR vacuum regulator duty cycle is high. The monitor compares the actual Differential Pressure Feedback EGR circuit voltage to a desired EGR flow voltage for that state to determine if EGR flow rate is acceptable or insufficient. This is a system test and may trigger a DTC for any fault causing the EGR system to fail.

    The DTC associated with this test is DTC P0401. DTC P1408 is similar to P0401 but performed during KOER Self-Test conditions.
  1. The MIL is activated after one of the above tests fails on two consecutive drive cycles.
0a01005.gif EGR Vacuum Regulator Solenoid The EGR vacuum regulator solenoid (Figure 88) is an electromagnetic device which is used to regulate the vacuum supply to the EGR valve. The solenoid contains a coil which magnetically controls the position of a disc to regulate the vacuum. As the duty cycle to the coil increases, the vacuum signal passed through the solenoid to the EGR valve also increases. Vacuum not directed to the EGR valve is vented through the solenoid vent to atmosphere. Note that at 0% duty cycle (no electrical signal applied), the EGR vacuum regulator solenoid allows some vacuum to pass, but not enough to open the EGR valve.

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Exhaust Gas Recirculation (EGR) Vacuum Regulator Solenoid Removal and Installation
  1. Disconnect the battery ground cable (14301). For additional information, refer to Section 414-01 .
  1. Disconnect the vacuum hoses and the EVR solenoid electrical connector.
  1. Remove the two nuts and the EVR solenoid (9J459).
From the looks of the rubber mounting, I would say it's mounted on the cowl (firewall) on the passenger side in the engine compartment.

Please rate as fixya if this helps. Thanks

Feb 24, 2009 | 2001 Ford Escort ZX2

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