P0401: Exhaust Gas Recirculation Flow Insufficient
Can you still drive? Yes, but the engine may knock under load. Prolonged knocking can damage internal engine components.
What Does P0401 Mean?
Code P0401 indicates that the EGR (Exhaust Gas Recirculation) system is not flowing enough exhaust gas back into the intake manifold. The EGR system reduces combustion temperatures and NOx emissions by recirculating a portion of exhaust gas. When the flow is insufficient, the ECM detects higher-than-expected combustion temperatures or uses a DPFE sensor to measure the shortfall.
Need to read your codes?
An OBD-II scanner lets you read and clear diagnostic trouble codes from your vehicle's computer. Most scanners work with any car made after 1996.
Browse OBD-II Scanners on AmazonCommon Causes
- Clogged EGR passages
- Faulty EGR valve
- Failed DPFE or EGR pressure feedback sensor
- Carbon buildup in intake manifold
- Vacuum supply issue to EGR valve
Symptoms
- Check engine light on
- Engine knocking or pinging under load
- Rough idle
- Failed emissions test for NOx
Diagnostic Steps
- 1Inspect EGR valve for carbon buildup
- 2Test EGR valve operation with vacuum pump
- 3Check DPFE or EGR pressure sensor readings
- 4Inspect and clean EGR passages in intake manifold
- 5Verify vacuum supply to EGR valve
- 6Monitor EGR flow data with scan tool
Recommended Parts & Tools
intake manifold gasket
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $100 - $800 |
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Chat with AI About P0401Commonly Affected Vehicles
Related Recalls
1 Active Recall — 2026 Ford F-150
The following NHTSA safety recalls have been issued for this vehicle. Contact your dealer to check if your vehicle is affected.
ELECTRICAL SYSTEM: INTEGRATED TRAILER BRAKE CONTROL
Ford Motor Company (Ford) is recalling certain 2021-2026 F-150, 2022-2026 F-250 SD, F-350 SD, F-450 SD, F-550 SD, Maverick, 2024-2026 Ranger, 2023-2026 F-600 SD, 2022-2027 Lincoln Navigator, Expedition, and 2026 E-Transit vehicles. When towing a trailer, the integrated trailer module (ITRM) may lose communication with the vehicle, possibly causing a loss of brake and turn signal lights, or a loss of brake function. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 108, " Lamps, Reflective Devices, and Associated Equipment."
Remedy: The integrated trailer module software will be updated by a dealer, or through an over-the-air (OTA) update, free of charge. Owner notification letters are expected to be mailed March 17, 2026. Owners may contact Ford customer service at 1-866-436-7332. Ford's number for this recall is 26C10. Vehicle Identification Numbers (VINs) involved in this recall will be searchable on NHTSA.gov beginning March 17, 2026.
Data provided by the National Highway Traffic Safety Administration (NHTSA).
Frequently Asked Questions
What does the EGR system do?
The EGR system recirculates a small amount of exhaust gas back into the engine to lower combustion temperatures and reduce harmful NOx emissions.
Can I clean the EGR valve instead of replacing it?
Yes, in many cases removing and cleaning the EGR valve with carburetor cleaner can resolve the issue and save you the cost of a new valve.
Community Fix Reports
Community reports are user-submitted and not verified by Auto AI Buddy. Results may vary.
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