P0400: Exhaust Gas Recirculation (EGR) Flow Malfunction
Can you still drive? Yes, the vehicle is safe to drive. You may notice engine knock under heavy acceleration. Avoid using full throttle to reduce the risk of detonation damage.
What Does P0400 Mean?
Code P0400 indicates that the ECM has detected that the EGR system is not flowing exhaust gas as expected. The EGR system recirculates a portion of exhaust gas back into the intake manifold to reduce combustion temperatures and lower NOx emissions. When the system does not flow properly, the code is set based on feedback from the DPFE sensor or intake manifold pressure changes.
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 in intake manifold
- Stuck-closed EGR valve
- Failed EGR valve diaphragm or motor
- Clogged or failed DPFE sensor
- Carbon buildup blocking EGR ports
Symptoms
- Check engine light on
- Engine knocking or pinging under acceleration
- Rough idle
- Increased NOx emissions
- Possible failed emissions test
Diagnostic Steps
- 1Test EGR valve operation by applying vacuum or commanding it open with a scan tool
- 2Monitor DPFE or MAP sensor readings when EGR is commanded open
- 3Inspect EGR passages in the intake manifold for carbon blockage
- 4Clean or replace the EGR valve
- 5Check EGR vacuum supply lines for leaks or blockages
- 6Inspect DPFE sensor hoses and replace if deteriorated
Recommended Parts & Tools
carbon cleaner
vacuum hand pump
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $100 - $600 |
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Chat with AI About P0400Commonly 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 is the EGR system?
The Exhaust Gas Recirculation system routes a small amount of exhaust gas back into the engine's intake to lower combustion temperatures. This reduces the formation of harmful nitrogen oxide (NOx) emissions.
Can I clean the EGR valve instead of replacing it?
Yes, in many cases cleaning the EGR valve and passages with carbon cleaner restores proper function. Heavy carbon buildup in the intake manifold EGR ports may require physical removal with picks and brushes.
Community Fix Reports
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