Most vehicles made in the past several decades are fitted with some sort of emission control components and systems. EGR or Exhaust Gas Recirculation is one such component. Just like any other part of the engine, these can fail. When that happens, they often trigger check engine light codes such as the P0401.
In this article, we’ll talk about the P0401 code, the common causes, symptoms, how to diagnose the issue, and what you’ll need to do to fix the issue.
What Is an EGR System, and How Does It Work?
The exhaust gas recirculation system was invented to reduce the volume of toxic gases that reach the atmosphere. This system works by sending a certain amount of exhaust gas back to the intake manifold from where they are pushed into the cylinders for another round of combustion.
The exhaust gas recirculation system is made out of three parts: the differential pressure sensor, actuator solenoid, the EGR valve and an EGR filter. These parts work in sync to provide the engine with exactly the right amount of exhaust gas at the right time. If any of these parts aren’t working as they should, the sensors in the EGR system will detect an issue and trigger a generic fault code such as the P0401.
What is the P0401 Code, and What Does It Mean?
The P0401 code stands for exhaust gas recirculation flow insufficient detected. What this means is that the EGR system isn’t sending the required amount of exhaust fumes back into the intake manifold, or isn’t doing it at the right time.
Even if some exhaust gas gets back to the intake manifold, it won’t work the way it should if the timing or amounts of gas are incorrect. There are a few reasons why this happens. Some of these can cause additional damage to other engine components if not addressed in a timely manner.
What Causes a P0401 Fault Code?
When it comes to the cause of the P0401 fault code, most reasons are related to carbon buildup. Carbon is a normal side effect of circulating exhaust gases. Given the fact that the exhaust gas recirculation system’s role is to send exhaust gas back to the intake manifold, it’s only a matter of time before the carbon buildup will cause an issue within the system.
Faulty EGR Valve
Another possible cause for the P0401 code is a faulty EGR valve. This part can also stick due to carbon buildup, but also wear. It’s recommended to clean the EGR valve every 20,000 miles or replace it if it’s stuck even after a thorough cleaning.
Vacuum Hose Leaks
Cracked or leaky vacuum hoses between the EGR valve and EGR control solenoid can also cause the P0401 code. If these hoses aren’t in perfect condition, the EGR valve won’t open all the way which can trigger this generic fault code. In some cases, it’s difficult to notice a small crack on one of these hoses, so checking them thoroughly is required.
What Are the Common Symptoms of P0401 Fault Code?
The first symptom you’ll notice when the code P0401 is triggered is the check engine light. It signals the driver about a possible issue with the car, and it should be checked as soon as possible. Just seeing the check engine light isn’t a symptom of one specific problem though, but a combination of other symptoms as well. If you scan the ECU with an OBD II scanner, you’ll have an idea what kind of issue triggered the check engine light in the first place.
The next thing you’ll notice is a drop in acceleration. A drop in fuel economy can also be a symptom of a P0401 fault code and eventually lead to a failed emissions test. A rough idle is another fairly common symptom of a faulty EGR system, as well as smoke coming out of the exhaust.
A lot of people have also reported a knocking noise while accelerating, which is a common symptom for the P0401 fault code.
Can EGR Cause No Start?
When the EGR valve is stuck open, it can cause the car to fail to start. Those that are able to start will likely notice a rough idle and smoke coming out of the exhaust.
Although failing to start the car because of this code is fairly uncommon, it’s still possible.
How to Diagnose and Fix P0401 Code
Diagnosing any generic fault code such as the P0401 starts with scanning the ECU with an OBD II scanner. This will tell you whether P0401 is the only code stored in the ECU or there are other fault codes causing your car to work out of the ordinary.
After reading the code with your OBD II scanner, continue visually inspecting the EGR system. You’ll need to inspect the EGR valve itself, the wiring, and vacuum hoses as well. If any of these parts are cracked or look suspicious, you’ll need to clean and/or replace them. Afterward, clear the code from the ECU to check if that particular part was causing the issue.
Make sure to inspect vacuum hoses thoroughly because spotting a hairline crack on the hoses can be extremely difficult. These small cracks can cause issues in the EGR system that can trigger the P0401 code.
After checking the EGR system for physical damage, continue looking for carbon buildup inside the EGR system parts. It’s common for the EGR valve to get stuck or even blocked due to carbon buildup. Fixing this includes cleaning the EGR valve with throttle cleaner thoroughly. All the carbon buildup should be removed before testing out the car. Make sure the EGR valve is completely dry before returning it to the car.
If none of these helps, you’ll need to remove the intake manifold and check for carbon buildup there as well. Before you can take the intake manifold off, you’ll need to disconnect all the cables, hoses, and remove the throttle body. Once you do, you’ll have clear access to the intake manifold, and you’ll be able to remove it from the car. Again, use a throttle body cleaner to clean the intake.
Since some intake systems can be pretty complex, it’s a good idea to keep a shop manual for your car, just in case you get stuck.
How do You Clean an EGR Valve Without Removing It?
Cleaning the EGR valve without removing it includes using a specialized EGR cleaner that comes in the form of a spray. Some people swear by it, while others think that only mechanically cleaning the EGR valve will give it back its full usability.
If you want to clean the EGR valve without removing it from the car, you’ll need to disconnect and remove the air filter. Then, you’ll need to start the car and get it at operating temperature. You’ll also need to have someone keep it idling at 2000 rpm.
Gently spray the cleaner in the intake hose in short bursts of less than a second until you use half of the aerosol. Every time you send some cleaner into the intake, your car will make a strange noise, but that’s fairly normal.
After you’ve finished spraying the cleaner, reconnect the air filter and leave your car idling for a few minutes. Take your car for a spin for 10-15 minutes without going over 3000 rpm. Once you’re back, clear the code with the OBD II scanner and check if it triggers the same P0401 code again.
Keep in mind that this procedure isn’t exactly recommended by the manufacturer, so proceed with it at your own risk.
Does P0401 Clear Itself?
Automatic code clearing depends on the make and model of your vehicle. Some cars are known to erase a fault code after the fix, while other cars require an OBD II scanner to erase the code manually.
Either way, it’s recommended to clear the P0401 code after attempting each fix, so you’ll know if a simple EGR valve cleaning fixed the issue you’re dealing with. If you fixed the faulty part, the code won’t return on its own, and you won’t need to erase the code manually again.
Can You Drive with P0401 Code?
The P0401 code is considered moderately severe, and you shouldn’t drive the car until the code is fixed. Because a faulty EGR system can cause damage to other internal parts of the engine, it’s not worth risking other, more expensive parts of an engine for an issue you can easily fix for $20 an hour of your time.
What If You Need To Replace Some Parts?
Although the P0401 fault code can be fixed by simply cleaning carbon buildup from the EGR system, fixing the issue might require you to completely replace a faulty part that’s causing the check engine light.
The intake system, with the EGR system included, is an important system that directly affects how the car runs. Using only genuine or OEM parts will ensure the car works the way it should. Here at eEuroparts.com, we offer one of the largest catalogs of Genuine, OEM, and quality aftermarket parts for a variety of European makes and models.
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