OBD-II, or Onboard Diagnostics, is a built-in engine computer that helps you detect your car’s problems in the form of multiple codes.
Whenever your OBD-II detects an error, it turns on the Check Engine light and gives you a certain code that indicates a specific error.
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 most common reasons for an EGR to malfunction revolve around the valve. It could happen due to:
- The EGR valve is clogged up and can’t allow the flow of exhaust gases.
- The EGR valve is faulty due to the low vacuum coming from the EGR control solenoid.
- The EGR can not hold the vacuum.
- Faulty DPFE (differential pressure feedback EGR) sensor
How Should I Expect When the Code P0401 Appears?
When a P0401 code pops up, there might not be many symptoms for you to notice. But, the following symptoms can indicate an EGR malfunction
- An illuminated Check Engine sign
- Pre-ignition knock or pinging when the car is accelerating
- An increase in fuel consumption
- Emission tests fail because of increased nitrous oxide exhaust
Is This Code Too Serious?
P0401 code is considered a serious one.
That’s why this code shouldn’t be left ignored for a long time.
But is it Risky For My Safety?
No, this code doesn’t pose a safety risk at all to you. But, if there are strong drivability issues, it’s better if you have it fixed as soon as possible.
Another Troubleshooting Code about Exhaust Gas Recirculation (EGR)
How Will My Mechanic Diagnose The Problem?
When the P0401 code pops up, the first thing your mechanic will do is to scan the codes and document the freeze frame data. This will help your mechanic verify the diagnosis and proceed from there.
After clearing the engine and making multiple road tests, your mechanic will check if the codes come back. If they do, he’ll start to visually scan your engine for damaged wires or worn-out connections.
Also, your mechanic will scan your vacuum hoses, wirings and connections to the EGR valve. After that, he’ll check the solenoid and the EGR temperature sensor.
Your mechanic will also want to make sure that your EGR valve is receiving enough engine vacuum, particularly when the control solenoid opens on light-to-medium acceleration.
Finally, your mechanic will remove your EGR temperature sensor and valve to check if there’s any carbon build-up or blockage of the EGR tubes.
How Can My Mechanic Fix These Problems?
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 or repair the clogged EGR valve
- Replace your EGR temperature sensor if it’s proved to lose its sensitivity.
- Replace the broken vacuum line to the EGR valve
Can My Mechanic Misdiagnose The Problem?
Unfortunately, it can get tricky when your mechanic is trying to figure out what exactly is causing your P0401 code. So these are common mistakes that your mechanic might make while diagnosing your P0401 code:
- Failing to clean the EGR tubes when replacing a defective valve
- Forgetting to test the EGR temperature sensor sensitivity and replacing a well functioning EGR valve
- Failing to check if your EGR control solenoid will hold the vacuum before replacing the valve
Voila! Your Car is All Set Up to Hit The Road
After you’ve got your P0401 code fixed, your car should be all cleared to get back in function again.
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.
You’ve learned that this code is serious, and it shouldn’t be left till it affects the drivability of your car.
James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.