What does p0401 EGR system insufficient flow detected mean?

So you have changed the EGR valve and this p0401 code continues to pop up on the computer. You are frustrated and ready to drive your car off of a cliff. What does this P0401 diagnostic trouble code mean anyway? The correct definition for this diagnostic trouble code P0401 is “ Insufficient EGR Flow Detected “.

What are the causes of the code p0401?

Causes of Code P0401 1 Clogged or restricted EGR passages due to excess carbon 2 Faulty EGR valve 3 EGR temperature sensor is covered with carbon

What can cause an EGR valve to malfunction?

EGR valves can malfunction by becoming stuck open or closed due to carbon buildup. When the trouble code P0401 is set, CO2 is reintroduced to the combustion chamber at the incorrect time or in incorrect amounts, which does not decrease the combustion temperature sufficiently enough to prevent the increase of NOx.

What is the diagnostic code for insufficient flow?

The correct definition for this diagnostic trouble code P0401 is “ Insufficient EGR Flow Detected “. YES.. your EGR valve could be bad causing this code.

What does p0401 mean on a Ford engine?

P0401 FORD Meaning Early Exhaust Gas Recirculation (EGR) systems component s include and EGR Valve, and Engine Control Μodule (ECΜ) Controlled Vacuum Switch Valve or EGR Solenoid and an EGR Vacuum Μodulator.

How can I tell if my EGR valve is bad?

However, the DPFE sensor is a much more common failure component that the EGR valve position sensor. How can I tell if my EGR valve is bad? There are two types of EGR valves. Both can go bad causing your P0401 code. There are electronic and vacuum operated EGR valves. Vacuum operated EGR valves are very easy to test.

Can a p0401 code still be stored in a computer?

If you have a P0401 code stored in the computer and have an electronic EGR valve but do not have a scanner to test it, you can still remove it and check for carbon stuck in the pintial of the EGR valve and even if the pintail moves up and down like it should. So my EGR valve checks out good but I still have this P0401 code?

Where are the EGR and dpfe sensors located?

The EGR valve position sensor is located right on the EGR valve itself while the DPFE sensor (Digital Pressure Feedback EGR) is separate from the EGR valve. It uses two hoses attached to the exhaust or exhaust manifold.

What causes insufficient EGR flow?

This type of problem can have a wide range of causes: A failing DPFE sensor Restricted or clogged EGR tubes A clogged catalytic converter Carbon buildup on the EGR temperature sensor Faulty or lack of vacuum supply to the EGR Electrical problems with the EGR circuit Problems with the engine computer

What is excessive EGR flow?

An EGR that has excessive flow can cause the engine to hesitate or stall on acceleration or have a very rough engine idle. The Check Engine Light on will cause the vehicle to fail emission testing. If the catalyst is blocked causing code, then it could cause engine to lose power or not start.

What is an EGR flow malfunction?

Exhaust Gas Recirculation (EGR) Flow Malfunction What does that mean? This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/model.

What causes p0401 code?

Code P0401 is triggered when the EGR temperature sensor does not see enough of a temperature change when the EGR is commanded to open. These sensors tend to get a lot of carbon buildup that causes them to lose sensitivity to the heat from the EGR gases.

What needs to be checked with the code p0401?

What needs to be checked with the code P0401: The most common problems with the EGR system is a faulty EGR valve and carbon deposits restricting the EGR flow. The EGR valve needs to tested.

What is the OBD code for insufficient EGR?

OBD II code P0401 Exhaust EGR Flow Insufficient The OBDII fault code P0401 means that the engine computer has detected that the Exhaust Gas Recirculation (EGR) system flow is insufficient. The EGR system redirects a small amount of exhaust gases back into the intake.

What causes the OBD code p0401 on a Mazda corolla?

A faulty VSV (Vacuum Switching Valve) for the EGR can also cause the code P0401 in older Toyota Corolla. Mazda: In many Mazda vehicles, the code P0401 could be caused by a bad EGR valve. Replacing the EGR valve with an updated part often solves the problem.

What could cause the code p0401?

What does code p0402 mean?

What the P0402 code means. P0402 is an OBD-II generic code that the engine control module (ECM) has detected indicating the engine exhaust gas recirculation ( EGR ) valve is flowing too much recirculated exhaust gases when it is commanded to open the flow of gases into the intake manifold.

What are the functions of the EGR valve?

The function of the EGR valve is to recirculate small amounts of exhaust back into the combustion chambers of the engine in order to decrease the combustion temperature, thereby reducing the formation of smog-producing nitrogen oxides. EGR valves can malfunction by becoming stuck open or closed due to carbon buildup.

What does p0404 OBD code mean?

OBD-II Code P0404 is defined as a Exhaust Gas Recirculation Circuit Range/Performance NOx gases, which cause acid rain and respiratory problems, are formed when the engine’s combustion temperature is too high (2500° F). EGR systems are used to reduce the combustion temperature, thus reducing NOx formation. Aug 12 2019

What kind of EGR valve does GM use?

Before we jump in head long into this article, you need to know that there are two types of electronic EGR valves that GM uses in most of their late model vehicles. The EGR valve that’s covered by this article are for 3.1L, 3.4L, and 3.5L GM vehicles from 2000 to 2009 models years (although some late 1999 models use this type of EGR valve too).

What does EGR stand for in engine p0401?

In this article, we are going to explore a few different possibilities that can cause this code as well as testing strategies to be able to diagnose and fix this P0401 code once and for all. EGR valve stands for Exhaust Gas re-circulation.

Is there a diagnostic code for insufficient EGR flow detected?

The correct definition for this diagnostic trouble code P0401 is “Insufficient EGR Flow Detected“. YES.. your EGR valve could be bad causing this code. But chances are there is going to be something more causing your computer to flag this p0401 code.

What does the DTC code p0401 stand for?

Diagnostic trouble code (DTC) P0401 stands for “Exhaust Gas Recirculation (EGR) Flow Insufficient Detected.” This code means that the computer detects insufficient exhaust gas recirculation (EGR) flow in the system.

Can a code p0401 cause excessive engine ignition?

Code P0401 can cause can cause excessive internal engine ignition and pre-ignition damage to the pistons and valves. Code P0401 Common Diagnosis Mistakes Replacing the EGR valve without checking the air passages of the intake manifold or the temperature sensor Code P0401 Diagnosis Steps

What causes a computer to flag a p0401 code?

The computer will flag your P0401 code in the computer when it recognizes that there is not enough exhaust gas going back through the intake chamber… or simply, a low flow which causes the computer to flag the P0401 code. How does your computer know how much exhaust gas is being burned if any? Different manufacturers do it differently.

What does the p0401 code mean on a car?

P0401 Code is relevant to your car’s EGR system. It lights up the Check Engine sign when the engine exhaust gas recirculation (EGR) valve isn’t pumping enough exhaust gases when it’s ordered to allow their flow into the intake manifold. What Causes My EGR to Malfunction?

The correct definition for this diagnostic trouble code P0401 is “ Insufficient EGR Flow Detected “. YES.. your EGR valve could be bad causing this code.

When to open the EGR valve when idle?

A good rule of thumb: If the EGR ports are clean, then the engine should stall or run very rough when opening up the EGR valve when the engine is at idle.

What does EGR stand for in an engine?

EGR valve stands for Exhaust Gas re-circulation. The Exhaust gas re-circulation valve takes exhaust gases from the exhaust manifold and puts them back into the intake chamber where they get sucked back into the engine and goes through the burning process for the second time.

What should be common knowledge of the EGR / DPF system on this engine?

What should be Common knowledge of the EGR/DPF system on this engine (this, i have posted before, just putting it here to start the thread)…

How does the EGR system work on a Ford?

In addition, some manufacturers (like Ford) use an EGR sensor or a DPFE sensor to tell the computer where the EGR valve is positioned or how much flow the EGR is currently flowing at any given time.

What is the EGR code on a Ford F250?

There are three main parts of the F250’s EGR system. They are the EGR Valve, Differential Pressure Sensor, and the Actuator Solenoid. P0401 is a general code, which means that regardless of the year (1996+ anyway) and the model, it’ll have the same meaning regardless of which manufacturer built the vehicle (Ford F250 or not).

What can cause an EGR valve to fail?

Damaged, split, cracked, dislodged, or perforated vacuum hoses/actuator actuator diaphragm that cause insufficient vacuum to operate the EGR valve actuator Failed or failing PCM, Note that this is a rare event, and the fault must be sought elsewhere before any control module is replaced How expensive is it to fix code P0401 ?

Where is the EGR valve located on a Ford?

EGR valves are almost always located on, or close to the inlet manifold, and can most commonly be recognized by a steel pipe that runs between the valve and the exhaust system/manifold. In the case of Ford applications, the PDFE sensor (the failure of which is a common cause of this code) is located on…

What’s the diagnostic code for the EGR valve?

Several technical service bulletins for a wide variety of different makes and models have documented different problems associated with the EGR valve system. With some exhaust gas issues you might set a diagnostic trouble code of PO401 or P0402.

A good rule of thumb: If the EGR ports are clean, then the engine should stall or run very rough when opening up the EGR valve when the engine is at idle.

What is the OBD2 code for Citroen EGR?

OBD2 Code P0401 Citroen definition: 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.

What to do about Ford Explorer p0401 insufficient flow?

Here are some of the most common fixes to help clear the P0401: Check the EGR Tube- It’s a good idea to check the tube going to the EGR because it’s often the cause of P0401, easy to do, fast, and replacing it is very affordable. If it’s cracked, you’ll need to get a new one.

What is the EGR valve on a Ford Explorer?

They are the EGR Valve, Differential Pressure Sensor, and the Actuator Solenoid. P0401 is a general code, which means that regardless of the year (1996+ anyway) and the model, it’ll have the same meaning regardless of which manufacturer built the vehicle (Ford Explorer or not).

What causes a p0401 code to be flagged?

If it does not see the right change in the o2 sensor signal, it will flag your P0401 code. Other manufacturers use the MAP sensor. When the EGR valve is commanded open by the computer, the manifold vacuum will change and MAP sensor signal will change.

What does a p0401 code on EGR mean?

So this sums up our guide to fix a persisting P0401 code. All you have to do is learn that a P0401 code means an insufficient EGR flow. This error may be due to some build-up carbon that clogged your EGR tubes, a faulty EGR valve, a damaged EGR solenoid, or even a damaged OBD-II.

How does the ECM know when EGR is flowing?

When EGR is flowing, the pressure will rise in the hose connected below the orifice and drop in the hose connected above it, thus the Engine Controller (ECM/PCM, etc.) can determine if EGR is flowing and how much.

What should I do if my EGR sensor is not working?

The most obvious thing to do is to clean the EGR tubes to the intake manifold and make sure there are no more remnants of carbon build-up over time. Also, according to your problem your mechanic will do one or some of the following: Replace your EGR temperature sensor if it’s proved to lose its sensitivity.

Why do I get a p0401 code on my engine?

Some manufacturers use the oxygen sensor to monitor the oxygen (air fuel) ratio in the exhaust as the engine is running. The computer will watch the o2 sensor signal as it commands the EGR valve open. If it does not see the right change in the o2 sensor signal, it will flag your P0401 code.

What causes the EGR to stop working on a Ford?

EGR flow malfunction could be caused by a clogged EGR valve or EGR tube. Before replacing any parts try cleaning the EGR valve, tube, and passages. If the tubes are clean you may have to replace the EGR Pressure sensor to fix the problem. The cost to diagnose the P0401 FORD code is 1.0 hour of labor.

What causes a Chevy Colorado p0401 to not start?

Check the tube and see if it is cracked, clogged or otherwise damaged. EGR Valve Itself is Bad – The EGR valve itself is usually not going to be the place to start. But, they certainly are the cause of P0401 often enough. Vacuum Issues – The EGR valve relies on engine vacuum to operate.

Why does my Chevy Captiva have a p0401 code?

EGR Valve Itself is Bad – The EGR valve itself is usually not going to be the place to start. But, they certainly are the cause of P0401 often enough. Vacuum Issues – The EGR valve relies on engine vacuum to operate. So, if you are encountering P0401 and other codes, the P0401 may be a symptom of larger problems.

What to do if your engine has insufficient EGR flow?

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

Why do I get an OBD code for insufficient EGR flow?

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 may not be opening due to a lack of vaccuum In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return.

How to fix Ford Ranger EGR insufficient flow?

The good news with P0401 is that it rarely ever costs much money to fix, and it is usually pretty easy to get the problem, since it is right on top of the engine. Most folks see P0401 Insufficient EGR flow, look up the price of an EGR valve, see how cheap it is and just throw a new one on. That can be a mistake.

What is OBD code p0401?

P0401 is a common OBDII trouble code that’ll pop up in the Ford Explorer. It has to do with the emissions system and stands for: P0401: EGR → Insufficient Flow.

What does a p0401 error code mean?

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.

How to fix p0401 Ford exhaust gas malfunction?

How do I fix code P0401 FORD Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector’s pins. P0401 FORD Tech Notes EGR flow malfunction could be caused by a clogged EGR valve or EGR tube.

What does p0401 stand for in Audi Q5?

P0401 is a common OBDII trouble code that’ll pop up in the Audi Q5. It has to do with the emissions system and stands for: The EGR system on a vehicle is responsible for recirculating exhaust gasses in order to lower the vehicles emissions output. There are three main parts of the Q5’s EGR system.

Where can I read the EGR code description?

To save money they take the car to aurozone or read the codes with a code reader. The code description is for a flow problem with the EGR.

What are the symptoms of a bad EGR valve?

Common Symptoms Of A BAD EGR Valve. The following are the most common symptoms that a Ford (or Mercury or Lincoln) car or truck will usually experience when there’s a fault in the EGR System: Car or truck runs fine, but the check engine light (CEL) is on with an EGR Valve Fault Code: P0401 EGR System Flow Insufficient.

When to test the Ford EGR valve solenoid?

The following are the most common symptoms that a Ford (or Mercury or Lincoln) car or truck will usually experience when there’s a fault in the EGR System: Car or truck runs fine, but the check engine light (CEL) is on with an EGR Valve Fault Code: P0401 EGR System Flow Insufficient. P01406 EGR Valve Pintle Position.

What causes Ford Taurus EGR to stop working?

EGR flow malfunction could be caused by a clogged EGR valve or EGR tube. Before replacing any parts try cleaning the EGR valve, tube and passages. If the tubes are clean you may have to replace the EGR Pressure sensor to fix the problem. There is a factory service bulletin for the following Ford models: 2000-2002 Ford Taurus

What are the symptoms of a Ford EGR fault?

The following are the most common symptoms that a Ford (or Mercury or Lincoln) car or truck will usually experience when there’s a fault in the EGR system: P0401 EGR System Flow Insufficient. P01406 EGR Valve Pintle Position. Rough Idle. Really bad gas mileage.

What does the OBDII fault code p0401 mean?

The OBDII fault code P0401 means that the engine computer has detected that the Exhaust Gas Recirculation (EGR) system flow is insufficient. The EGR system redirects a small amount of exhaust gases back into the intake. Read more how the EGR system works in this article. – clogged or restricted EGR passages.

What is the EGR code on a Ford F350?

There are three main parts of the F350’s EGR system. They are the EGR Valve, Differential Pressure Sensor, and the Actuator Solenoid. P0401 is a general code, which means that regardless of the year (1996+ anyway) and the model, it’ll have the same meaning regardless of which manufacturer built the vehicle (Ford F350 or not).

To save money they take the car to aurozone or read the codes with a code reader. The code description is for a flow problem with the EGR.

How does an EGR sensor work on a car?

When the EGR valve is commanded open by the computer, the manifold vacuum will change and MAP sensor signal will change. In addition, some manufacturers (like Ford) use an EGR sensor or a DPFE sensor to tell the computer where the EGR valve is positioned or how much flow the EGR is currently flowing at any given time.

What can I do about insufficient EGR flow?

Use vacuum pump to open the EGR valve while monitoring the DPFE voltage and RPM engine. Clean the EGR valve and tubing to remove the deposits Check the voltage at DPFE and compare to specified values, You can also refer to your repair manual for your specific model Replace your DPFE sensor with high quality one

What causes a p0401 Ford to run out of gas?

P0401 FORD Possible Causes 1 EGR passage clogged 2 Faulty EGR Vacuum Modulator Valve 3 Faulty EGR Valve 4 Faulty EGR solenoid valve 5 EGR solenoid valve harness is open or shorted 6 EGR solenoid valve circuit poor electrical connection 7 Dead (Weak) battery 8 Faulty EGR temperature sensor and circuit 9 Exhaust gas leaks

How much does it cost to diagnose Ford code p0401?

Cost of diagnosing the P0401 FORD code Labor: 1.0 The cost of diagnosing the P0401 FORD code is 1.0 hour of labor. The auto repair labor rates vary widely across the country, and even within the same city. Most auto repairs shops charge between $75 and $150 per hour. When is the P0401 FORD code detected? Low EGR flow control is detected

How does early exhaust gas recirculation SYSTEM ( EGR ) work?

P0401 FORD | Exhaust Gas Recirculation Flow Insufficient Detected | Early Exhaust Gas Recirculation (EGR) systems component s include and EGR Valve, and Engine Control Μodule (ECΜ) Controlled Vacuum Switch Valve or

What causes a p0304 problem on a Ford F150?

There are quite a few things that can cause the P0304 trouble code to trigger the Ford F150. Here are the most common problems that will throw the code. They are presented somewhat in order from most to least likely to be causing the code: Bad Spark Plugs – Spark plugs are one of the most common causes of P0304.

What does p0305 mean on Ford cylinder 5?

The P0305 code means that cylinder 5 is misfiring or is randomly misfiring. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder 5. If the problem persists more tests needs to be done to diagnose the problem, see “Possible Causes”

What causes an EGR code to be misfired?

Defective DPFE sensor in the EGR system causing EGR codes are often occurs on Ford vehicles. Misfire codes P0171 or P0174 indicated the engine too much air and/or engine is not enough fuel (fuel mixture running lean).

What is the EGR code on a Ford F150?

There are three main parts of the F150’s EGR system. They are the EGR Valve, Differential Pressure Sensor, and the Actuator Solenoid. P0401 is a general code, which means that regardless of the year (1996+ anyway) and the model, it’ll have the same meaning regardless of which manufacturer built the vehicle (Ford F150 or not).

Why does my Ford F150 have insufficient flow?

That’s because the EGR valve is not always going to be the culprit. Here are some of the most common fixes to help clear the P0401: Check the EGR Tube- It’s a good idea to check the tube going to the EGR because it’s often the cause of P0401, easy to do, fast, and replacing it is very affordable. If it’s cracked, you’ll need to get a new one.

What does p0401 stand for on a Ford F150?

P0401 is a common OBDII trouble code that’ll pop up in the Ford F150. It has to do with the emissions system and stands for: It has to do with the emissions system and stands for: P0401: EGR → Insufficient Flow

What does EGR stand for on an OBD-2?

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/model. EGR stands for Exhaust Gas Recirculation.

What is the diagnostic code for excessive EGR?

It is one of the generic diagnostic trouble codes in a number of makes and models that are related to the vehicle’s EGR. Code P0402 indicates that your car computer has detected excessive EGR.

In addition, some manufacturers (like Ford) use an EGR sensor or a DPFE sensor to tell the computer where the EGR valve is positioned or how much flow the EGR is currently flowing at any given time.

Why is EGR important to the p0401 code?

Usually on an OBD2 system that sets the P0401, the ECM/PCM must see the failure on two consecutive trips before it will permanently set the code and trigger the Check Engine Light. The EGR system is important because it reduces emissions by allowing burnt exhaust gas to flow back into the engine.

What is the EGR code for insufficient flow?

The code relates to flow from the EGR to the intake. Remove EGR and throttlebody and clean the ports with intake cleaner and a scribe or snake. Also check for leaking gaskets or lines but usualy the system is just CLOGGED with hard carbon. Remove clog and flow will return and your light will not come back on. Loading…

What are the results of the GM EGR valve test?

Check engine light (CEL) will be shining nice and bright. P0401 EGR System Flow Insufficient. P0403 EGR Solenoid Control Circuit. P0404 EGR Open Position Performance. P0405 EGR Position Sensor Circuit Low Voltage. Rough idle. Really bad gas mileage.

Why is my Ford F150 p0401 not starting?

Check the tube and see if it is cracked, clogged or otherwise damaged. EGR Valve Itself is Bad– The EGR valve itself is usually not going to be the place to start. But, they certainly are the cause of P0401 often enough. Vacuum Issues– The EGR valve relies on engine vacuum to operate.

Why does my Hyundai Santa Fe have a p0401 code?

So, if you are encountering P0401 and other codes, the P0401 may be a symptom of larger problems. For instance, if the motor is not running well enough to create sufficient vacuum to operate the EGR valve, than P0401 will often be thrown.

Check the tube and see if it is cracked, clogged or otherwise damaged. EGR Valve Itself is Bad– The EGR valve itself is usually not going to be the place to start. But, they certainly are the cause of P0401 often enough. Vacuum Issues– The EGR valve relies on engine vacuum to operate.

What causes the p0401 code on a Ford Ranger?

Diagnosing what is causing the P0401 code in the Ranger is typically not very tricky. Here are the most common causes: Blocked EGR Tube – The tube that carries the exhaust gases back to the motor may clog up over time. Alternatively, it can become bent or kinked.

Why does my Ford Ranger have a p0401 code?

What could cause the P0401 code: When certain driving conditions are met and the computer wants exhaust gas recirculation, it provides a pulsing voltage to the electronic vacuum regulator (EVR). The EVR is a solenoid valve.

What is the trouble code on my 1996 Ford Ranger?

Getting my 1996 Ford Ranger ready to pass a state emission inspection, I had to diagnose Ford trouble codes P0401 and P1443. What could cause the P1443 code:

Causes of Code P0401 1 Clogged or restricted EGR passages due to excess carbon 2 Faulty EGR valve 3 EGR temperature sensor is covered with carbon

What does fault code p0401 on OBD II mean?

What Does Code P0401 Mean? OBD II fault code P0401 is a generic code that is defined as “ EGR Insufficient Flow Detected”, and is set when the PCM (Powertrain Control Module) detects a lower than expected flow of exhaust gas through the EGR (Exhaust Gas Recirculation) system.

What does p0401 insufficient EGR flow mean?

P0401 Insufficient EGR Flow 1 Technical Description. What does that mean? 2 Symptoms. You may notice drivability problems such as pinging (a.k.a. 3 Causes 4 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.

What does the OBD code p0404 mean?

What the P0404 code means. P0404 is an OBD-II generic code that the engine control module (ECM) detected the engine exhaust gas recirculation (EGR) valve or sensor is out of specification range or its performance has gone out of specification parameters.

What does p0404 mean on an EGR sensor?

Often times code P0404 does not actually indicate that there is something wrong with the EGR valve itself, but actually that the EGR sensor is telling your PCM that the proper amount of EGR needed to flow back into your cylinders and cool them is not present.

Are there any symptoms of a p0404 DTC?

There may be no symptoms of a P0404 DTC other than the MIL (malfunction indicator lamp) or check engine light. However, Exhaust Gas Recirculation systems are inherently problematic due to carbon buildup in the intake manifold, etc.

What is the code for insufficient flow on a check engine light?

Someone gets a check engine light. To save money they take the car to aurozone or read the codes with a code reader. The code description is for a flow problem with the EGR.

How to test an electrically actuated EGR valve?

Before you go ripping the EGR off, be sure that it is getting the electricity that it needs first. You can test all cables of the EGR by back probing them with a multimeter to see if they have the right voltage. Shown below is an excellent video showing how to test an electrically actuated EGR valve.

What does p0401 EGR system insufficient flow detected mean?