P0401 Exhaust gas recirculation (EGR) flow insufficient detected

EGR flow insufficient

Monitor

P0401 is an emissions fault: the computer sees less exhaust gas recirculation than it asked for. The car usually drives normally, though too little EGR can bring on pinging under load, so it can be watched and fixed without urgency unless symptoms appear.

It gets more serious if:

  • Inspect soon: Have it inspected soon if the engine knocks or pings under load, runs rough, hesitates or loses power. Too little EGR can cause knocking, and an EGR valve stuck open causes rough running and low power.
  • Stop: If the check engine light starts flashing, pull over when safe and let the engine cool, as Honda's manual instructs for a blinking light.

Source: how we rate severity

P0401 in short

P0401 means the engine computer measured less exhaust gas recirculation flow than it asked for. Carbon clogging the EGR passages or valve is the most common cause, followed by a failed valve or a vacuum supply fault. The car usually drives normally, so it can be fixed without urgency unless it knocks or loses power.

The EGR system feeds a small, metered amount of exhaust back into the intake. This lowers combustion temperatures, which cuts nitrogen oxide emissions and helps prevent knocking.

Emissions rules require the engine computer to watch EGR flow and set a code when flow falls too low. P0401 is that low-flow code. It does not mean anything is damaged yet; it means the EGR gas is not getting through as it should.

Carbon build-up is the classic cause. Over time it narrows the passages and can stop the valve from opening fully. On older systems a cracked vacuum hose or a failed solenoid can also keep the valve shut.

Most likely causes

  1. Carbon clogging the EGR passages or valve

    Common general cause
    Why it ranks here
    Delphi names carbon build-up as the biggest cause of EGR failure. It restricts the ports and stops the valve from opening fully.
    What would change this
    Rises on higher-mileage engines and if heavy carbon is seen when the valve is removed. Falls if the passages are clean.

  2. Failed or sticking EGR valve

    Common general cause
    Why it ranks here
    A valve that does not open, or opens too little, gives low flow. Hyundai and Toyota have issued bulletins replacing the EGR valve for P0401 on some models.
    What would change this
    Rises if the valve does not move when commanded or a bulletin covers your car. Falls if it moves freely and flow returns.

  3. Vacuum hose or EGR solenoid fault (vacuum-operated systems)

    Common general cause
    Why it ranks here
    On vacuum-operated valves a cracked, loose or mis-routed hose, or a failed control solenoid, keeps the valve from opening. Ford has a bulletin for a mis-routed vacuum harness causing P0401.
    What would change this
    Rises if a hose is cracked, off or routed wrongly, or the valve opens when vacuum is applied directly.
    How to test the vacuum hoses and intake leaks

  4. Restricted EGR cooler or intake fitting (some models)

    Supported by vehicle data
    Why it ranks here
    Ford has a bulletin for a restricted EGR cooler on the 2011–2012 Super Duty, and Nissan has one for a restricted EGR fitting on the 2023 Rogue intake air duct, both setting P0401.
    What would change this
    Rises on those models or if the valve works but flow is still low.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read the codes and freeze frame, then ask a dealer whether your VIN has a bulletin or warranty extension for P0401. Hyundai, Nissan, Toyota, Ford and Honda have issued them.

    Low riskTool: OBD-II scan tool

  2. With the engine off and cool, look at any vacuum hoses running to the EGR valve and its solenoid for cracks, loose ends or wrong routing.

    Low riskTool: flashlight

  3. Have a shop open the EGR valve with a scan tool or a hand vacuum pump at idle and watch how the engine responds.

    Best left to a shopTool: bidirectional scan tool or hand vacuum pump

    Warning:The engine runs during this test and the EGR valve and exhaust parts get very hot. Leave it to someone trained.

Symptoms

  • Check engine light with no change in how the car drives
  • Pinging or knocking when accelerating or climbing hills Gets more serious: stop and have it checked.
  • Rough running, hesitation or loss of power Gets more serious: stop and have it checked.
  • Flashing check engine light Gets more serious: stop and have it checked.

Compare with: Rough idle with the check engine light on

How to fix

  1. With the engine off and cool, look over the vacuum hoses at the EGR valve for cracks or a hose that has come off.

  2. Ask a dealer whether your VIN has an open bulletin or warranty extension for P0401.

On your vehicle

Hyundai

  • 2020–2021 · Sonata · 2.5 GDI

    Supported by vehicle data

    Hyundai bulletin 23-EE-009H covers EGR valve replacement for P0401 on the 2020–2021 Sonata 2.5 GDI. Whether the bulletin is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 23-EE-009HStatus unverified

    P0401, EGR valve replacement

    2020–2021sonata · 2.5 GDI · issued · NHTSA 10241875

    Hyundai gives an EGR valve replacement for P0401 on the 2020–2021 Sonata 2.5 GDI.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Nissan

  • 2023 · Rogue

    Supported by vehicle data

    Nissan bulletin NTB23-015 traces low EGR flow on the 2023 Rogue to a restricted EGR fitting on the intake air duct, fixed by replacing the duct. Whether the bulletin is still current is not verified.

  • NTB23-015Status unverified

    Restricted EGR fitting on the intake air duct

    2023rogue · issued · NHTSA 10232676

    A restricted EGR fitting on the intake air duct can cause low EGR flow. Nissan says to replace the duct.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Toyota

  • 2010–2012 · Prius · 2ZR-FXE

    Supported by vehicle data

    Toyota bulletin T-SB-0075-13 supplies an improved EGR valve for P0401 on the 2010–2012 Prius and 2012 Prius v. Whether the bulletin is still current is not verified.

  • T-SB-0075-13Status unverified

    P0401, improved EGR valve

    2010–2012prius, prius-v · 2ZR-FXE · issued · NHTSA 10132025

    Toyota released an improved EGR valve for P0401 on the 2010–2012 Prius and 2012 Prius v.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Ford

  • 2011–2012 · F-250 Super Duty

    Supported by vehicle data

    Ford bulletin 13-6-5 links P0401 on the 2011–2012 F-250 Super Duty, and larger Super Duty models, to a restricted EGR cooler core. Whether the bulletin is still current is not verified.

  • 2007 · Ranger

    Supported by vehicle data

    Ford bulletin 061711 traces P0401 on the 2007 Ranger to a mis-routed vacuum harness. Whether the bulletin is still current is not verified.

  • TSB-13-6-5Status unverified

    P0401 from a restricted EGR cooler core

    2011–2012f-250 · issued · NHTSA 10053084

    A restricted EGR cooler core can set P0401 on 2011–2012 Super Duty trucks. The NHTSA record lists the F-250 SD, F-450 SD, F-550 SD, F-650 SD and F-750 SD.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 061711Status unverified

    P0401 from a mis-routed vacuum harness

    2007ranger · NHTSA 10021039

    A mis-routed vacuum harness can set P0401 on the 2007 Ranger. The NHTSA record gives no issue date.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Honda

  • 1999–2003 · Odyssey

    Supported by vehicle data

    Honda bulletin 00009 extended the warranty for EGR valve contamination or port clogging on the 1999–2003 Odyssey and 2003 Pilot, with P0401 or P1491. The extension was issued in 2005; whether it still applies is not verified.

  • 00009Status unverified

    Warranty extension for EGR valve contamination or port clogging

    1999–2003odyssey, pilot · issued · NHTSA 10017431

    Covers 1999–2003 Odyssey and 2003 Pilot with P0401 or P1491, or hesitation or surge, from EGR valve contamination or port clogging.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P1285Cylinder head temperature above the engine computer’s limit (Ford, Lincoln, Ford-built Mazda)

    Shares causes Supported by vehicle data

    Ford SSM 48345 lists P0401 with P1285 when a 2019–2020 2.0L EcoBoost EGR cooler leaks coolant.

All Turbocharging, fuel pressure and EGR codes

P0401 questions

Is it safe to drive with P0401?

Usually, for a while. It is an emissions fault and most cars drive normally. Have it checked soon if the engine pings, runs rough or loses power, and pull over if the check engine light flashes.

Will cleaning the EGR valve fix P0401?

Sometimes. Carbon is the most common cause, so cleaning the valve and passages can restore flow. If the valve itself has failed, or the passages are badly clogged, parts may be needed.

Sources and review

  1. Final Regulation Order: 13 CCR §1968.2, Malfunction and Diagnostic System Requirements (OBD II), 2004 and subsequent model-year passenger cars, light-duty trucks and medium-duty vehicles (2015 amendments) — California Air Resources Board
  2. The basics of EGRs - what they do, how they work, how to troubleshoot — Delphi Technologies
  3. 2023 Integra Owner's Manual: Indicator, Coming On/Blinking — American Honda Motor Co.
  4. Honda warranty extension 00009: EGR valve contamination or EGR port clogging can cause P0401, P1491 or hesitation/surge (1999–2003 Odyssey, 2003 Pilot) — American Honda Motor Co. / NHTSA ,
  5. Hyundai 23-EE-009H: EGR valve replacement for P0401 EGR flow insufficient (2020–2021 Sonata 2.5 GDI) — Hyundai Motor America / NHTSA ,
  6. Toyota T-SB-0075-13: MIL on with P0401, improved EGR valve (2010–2012 Prius and 2012 Prius v, 2ZR-FXE) — Toyota Motor Sales / NHTSA ,
  7. Ford 061711: MIL on with P0401 from a mis-routed vacuum harness (2007 Ranger) — Ford Motor Company / NHTSA
  8. Ford TSB 13-6-5: MIL with P0401 from a restricted EGR cooler core (2011–2012 F-Super Duty) — Ford Motor Company / NHTSA ,
  9. Nissan NTB23-015: MIL on with P0401, restricted EGR fitting on the intake air duct (2023 Rogue) — Nissan North America / NHTSA ,
  10. Ford SSM 48345: 2.0L EcoBoost EGR cooler leaking coolant (2019–2020 Edge, Escape, Nautilus, Corsair) — Ford Motor Company / NHTSA ,
  11. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
Last reviewed
Written by
Saurabh K.
Editorial review
Pending
Technician review
Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

My Car

Pick your car and code pages will point out notes and bulletins for it. Saved only in this browser.

Fill this in from your VIN

Used once to identify your engine; not stored.