P0401
Fix within 1-2 weeksYour engine's Exhaust Gas Recirculation (EGR) system isn't flowing enough exhaust gas.
Code P0401 means your engine's EGR system has insufficient exhaust gas flow. Common causes: Clogged EGR passages (40%), faulty EGR valve (30%). Drivability: Yes, safe to drive. Repair cost: $50-$250 DIY, $150-$600 professional.
Can I Drive With P0401?
Yes, safe to drive
No restrictions, but fix within 1-2 weeks to avoid further issues and pass emissions.
Stop driving immediately if: Engine is severely knocking, stalling frequently, or experiencing significant power loss.
Symptoms of P0401
- 1Check Engine Light is on
- 2Rough or unstable idle
- 3Engine hesitation or stumbling during acceleration
- 4Engine pinging or knocking (pre-ignition)
- 5Reduced fuel economy
- 6Engine stalling at idle
Common Causes of P0401
Parts most likely causing this code, ranked by probability
Carbon buildup restricts the flow of exhaust gas through the EGR system, preventing the engine from receiving the commanded amount.
40% of P0401 cases are fixed by cleaning or replacing clogged EGR passages
The EGR valve can stick closed due to carbon buildup or fail electronically, preventing exhaust gas from recirculating.
30% of P0401 cases are fixed by replacing the EGR valve
This sensor measures the pressure difference across the EGR system to determine flow; a faulty sensor reports incorrect flow to the computer.
15% of P0401 cases are fixed by replacing the DPFE sensor (common on Ford vehicles)
On vacuum-operated EGR systems, this component controls the vacuum to the EGR valve; if it fails, the valve won't open.
10% of P0401 cases are fixed by replacing the EGR solenoid or transducer
A vacuum leak in the lines controlling a vacuum-operated EGR valve prevents the valve from opening fully or at all.
5% of P0401 cases are fixed by repairing vacuum leaks
Check These First (Before Buying Parts)
- 1. Visually inspect all vacuum lines connected to the EGR valve or solenoid for cracks, disconnections, or signs of wear.
- 2. Check the electrical connector at the EGR valve or solenoid for corrosion or loose pins.
- 3. Listen for any obvious vacuum leaks around the intake manifold or EGR system components with the engine running.
How to Diagnose P0401
- 11. Visually inspect the EGR valve and its associated vacuum lines (if applicable) for damage or disconnections.
- 22. Remove the EGR valve and inspect the valve and the intake manifold passages for heavy carbon buildup. Clean thoroughly if clogged.
- 33. Test the EGR valve operation. On vacuum-operated systems, apply vacuum to the valve to see if it opens and holds vacuum. On electronic valves, use a scan tool to command it open and listen for movement.
- 44. Test the DPFE sensor (if equipped) by monitoring its voltage output with a multimeter or scan tool as the EGR valve opens.
- 55. Check for proper voltage and ground at the EGR valve or solenoid connector. Inspect wiring for damage.
P0401 on Popular Vehicles
Ford F-150
1997-2010P0401 is very common on these trucks. The DPFE sensor is a frequent culprit, often failing due to moisture or corrosion. Clogged EGR passages are also a significant cause.
60% fixed by replacing DPFE sensor or cleaning passages
Honda Accord
1998-2007Carbon buildup in the EGR port on the intake manifold is a very common issue, especially on 4-cylinder engines. The EGR valve itself can also fail due to carbon.
70% fixed by cleaning EGR passages or replacing EGR valve
Chevrolet Silverado
1999-2013P0401 on these trucks often points to a faulty EGR valve or significant carbon buildup in the EGR tube and intake manifold passages. Vacuum leaks are less common but should be checked.
65% fixed by replacing EGR valve or cleaning passages
Frequently Asked Questions
What does P0401 mean?
P0401 indicates that the engine computer has detected insufficient flow in the Exhaust Gas Recirculation (EGR) system. This means the engine is not getting enough exhaust gas recirculated back into the intake manifold when commanded.
Can I drive with P0401?
Yes, you can drive safely with a P0401 code. However, you should fix it within 1-2 weeks to prevent potential engine knocking, reduced fuel economy, and to ensure your vehicle passes emissions tests.
Will P0401 clear itself?
No, P0401 will not clear itself. The underlying issue, such as carbon buildup or a faulty component, must be addressed. Once the repair is made, you can clear the code with an OBD-II scanner, or it will clear after several drive cycles if the problem is resolved.
How do I fix P0401 myself?
You can fix P0401 yourself by first inspecting and cleaning the EGR valve and its passages for carbon buildup. If cleaning doesn't work, you may need to replace the EGR valve, EGR solenoid, or the DPFE sensor, depending on your vehicle's system and diagnosis.
How much does it cost to fix P0401?
DIY repair costs for P0401 are typically $50-$250, mainly for parts like an EGR valve or DPFE sensor, plus carbon cleaner. Professional shop repairs cost $150-$600, covering parts and labor for diagnosis and replacement.
P0401 keeps coming back - why?
P0401 keeps coming back because the root cause was not fully addressed. This often happens if only the EGR valve was replaced but the passages remained clogged, or if a faulty sensor (like the DPFE) was overlooked. A thorough cleaning of all EGR passages is critical.
Will P0401 fail emissions/smog test?
Yes, a P0401 code will cause your vehicle to fail an emissions or smog test. The EGR system is a critical component of your vehicle's emissions control, and a fault indicates it's not operating correctly.
What's the difference between P0401 and P0400?
P0400 indicates a general 'EGR Flow Malfunction,' meaning the computer detected an issue with the EGR system's operation. P0401 is more specific, indicating 'EGR Flow Insufficient Detected,' meaning the system is not flowing enough exhaust gas.
P0401 on Ford F-150?
On many Ford F-150 models, especially those from the late 90s to mid-2000s, P0401 is frequently caused by a faulty Differential Pressure Feedback EGR (DPFE) sensor or clogged EGR passages. The DPFE sensor is a common failure point on these trucks.
Questions to Ask Your Mechanic
Did you inspect the EGR passages in the intake manifold for carbon buildup, not just the valve?
Good answer: Yes, we removed the EGR valve and thoroughly cleaned the intake manifold ports and the EGR tube. They were heavily restricted.
What were the readings from the DPFE sensor (if applicable) when the EGR valve was commanded open?
Good answer: The DPFE sensor was showing a flat line or incorrect voltage when the EGR valve was commanded open, indicating it wasn't detecting flow, even after the valve was confirmed to be working.
Repair Cost Estimate
DIY Repair
Parts only
$50-$250
Shop Repair
Parts + labor
$150-$600
Save $100-$350 by doing it yourself
Difficulty
intermediate
Time
1-3 hours
Intermediate - requires some mechanical aptitude for disassembly and cleaning, and potentially a scan tool for testing.
Cost of Waiting
Ignoring P0401 leads to reduced fuel economy, potential engine knocking or pinging (which can damage engine components over time), and a guaranteed failure of emissions tests. A $50-$250 repair now prevents more expensive engine damage or repeated emissions test failures.
While You're In There...
Always replace the gasket when removing or replacing the EGR valve to ensure a proper seal and prevent exhaust leaks.
If you're cleaning carbon from the intake, it's a good time to clean the throttle body as well, as carbon buildup there can also affect idle quality.
Tools You'll Need
- Basic hand tools (sockets, wrenches)
- Carbon cleaner spray
- Wire brush or pipe cleaners
- Vacuum pump (for testing vacuum EGR valves)
- OBD-II scan tool (to clear code and monitor data)
- Multimeter (for electrical testing)
P0401 is a very common emissions code. Most repairs involve cleaning carbon or replacing a single component, and your engine will run much smoother and more efficiently afterward.
- Family-owned since 1957
- 990,000+ happy customers
- Fast nationwide shipping
- Easy returns
Your Next Steps
Step 1: Inspect the EGR valve and its associated passages for heavy carbon buildup. This is the most common cause.
Step 2: If carbon is present, thoroughly clean the EGR valve and all accessible passages. If the valve is stuck or fails electrical tests, replace it.
Step 3: If cleaning and valve replacement don't fix it, test the DPFE sensor (if equipped) or the EGR solenoid/transducer and replace if faulty. Parts you'll likely need: EGR valve, EGR valve gasket, carbon cleaner, or a DPFE sensor.