P0401 fault code: what it means

P0401: Not enough EGR flow. Very common on diesels and direct-injection engines from carbon build-up.

Engine and gearbox (powertrain) · Minor

Usual causes, most likely first

carbon-clogged EGR valve or passages
EGR valve stuck closed
blocked EGR cooler
faulty EGR position or pressure sensor

P0401 by make

Audi

EGR flow too low. On TDI usually a soot-blocked EGR valve or cooler; on common-rail TDI the EGR filter can block after a DPF regen with high soot load.

Usual causes: soot-blocked EGR valve or cooler; blocked EGR filter (common-rail TDI, often after high DPF soot load); EGR valve stuck or faulty; exhaust pressure flap control module (J883) fault (2009-2012 2.0 CR TDI)

BMW

Diesel EGR flow too low. On BMW diesels (N47 / N57) the EGR valve and cooler soot up; BMW recalled many 2010-17 diesels for EGR cooler glycol leaks.

Usual causes: EGR valve clogged with soot; leaking or blocked EGR cooler (check recall); EGR position sensor or wiring; boost or vacuum leak

Ford

EGR flow too low. On Ranger/Everest 3.2 and 2.2 the EGR valve and cooler clog with soot; a leaking cooler can also put coolant into the engine.

Usual causes: EGR valve clogged with soot; blocked EGR cooler; EGR valve not opening

GWM

EGR flow insufficient. GW4D20 diesels are known for soot-blocked EGR.

Usual causes: soot-blocked EGR valve; blocked EGR cooler or passages; sticking EGR valve

Honda

EGR flow too low. On older Honda V6 (e.g. 1998-2001 Accord V6) carbon clogging the EGR port in the intake manifold is a known cause, not just the valve.

Usual causes: carbon-blocked EGR port in intake manifold; faulty EGR valve; blocked EGR pipe

Isuzu

EGR flow insufficient. 4JJ1/4JJ3 EGR valve and cooler soot up.

Usual causes: soot-blocked EGR valve; blocked EGR cooler; sticking EGR valve

Jeep

EGR flow insufficient (CRD diesel).

Usual causes: soot-blocked EGR valve or cooler; sticking EGR valve; blocked EGR passage

Kia

EGR flow insufficient (diesel and some petrol engines).

Usual causes: carbon-clogged EGR valve; blocked EGR passages or cooler; EGR valve position sensor or wiring fault

Land Rover

EGR flow insufficient. The ECU sees less exhaust gas recirculation than expected.

Usual causes: soot-blocked EGR valve or cooler; sticking EGR valve; blocked EGR passage

LDV

EGR flow insufficient.

Usual causes: soot-blocked EGR valve; blocked EGR cooler or passages; sticking EGR valve

Lexus

EGR flow insufficient. On CT200h (2ZR-FXE) almost always heavy carbon clogging the EGR valve, cooler and intake passages; Lexus issued TSBs and an updated valve.

Usual causes: carbon-clogged EGR cooler and intake EGR passages; sticking EGR valve; MAP sensor reading wrong

Mazda

SkyActiv-D: EGR flow too low. Soot build-up in the EGR valve and passages is common on short-trip diesels.

Usual causes: EGR valve stuck closed / carboned up; soot blocking EGR passages or cooler; intake leak between turbo and intake manifold; intake shutter valve or sensor signal fault

Mercedes-Benz

EGR flow too low. On OM651/OM642 usually a carboned-up EGR valve or cooler.

Usual causes: carbon-fouled EGR valve; clogged EGR cooler; heavy intake carbon deposits

Mini

Diesel EGR flow too low (Cooper D / SD, Countryman D). EGR valve and cooler soot up; BMW group recalled many 2010-17 diesels over EGR cooler leaks.

Usual causes: EGR valve clogged with soot; EGR cooler leaking or blocked (check recall); EGR position sensor or wiring

Mitsubishi

EGR flow too low. On 4N15 / 4D56 diesels the EGR valve and intake fill with carbon; poor response from low revs.

Usual causes: carbon-clogged EGR valve; carbon-blocked EGR passages / intake manifold; sticking EGR valve motor or solenoid; blocked EGR cooler or pipe

Nissan

EGR flow too low. On YD25 Navara usually a carbon-blocked or stuck-closed EGR valve, or a blanking plate fitted.

Usual causes: EGR valve stuck closed / carbon blocked; carbon build-up in intake and EGR passages; EGR blanked off without a tune

Skoda

EGR flow too low. On TDI usually a soot-blocked EGR valve or cooler; on common-rail TDI the EGR filter can block after a DPF regen with high soot load.

Suzuki

EGR flow insufficient. Suzuki M15A/M16A engines use a stepper EGR valve that clogs with carbon.

Usual causes: carbon-blocked EGR valve; blocked EGR passages; failed EGR stepper motor

Toyota

EGR flow insufficient. On Prius/Corolla/C-HR hybrids with the 2ZR-FXE this is usually heavy carbon blocking the EGR cooler, valve and intake passages.

Usual causes: carbon-clogged EGR cooler and intake EGR passages (2ZR-FXE hybrids); sticking EGR valve; MAP sensor reading wrong

Volkswagen

EGR flow too low. On TDI usually a soot-blocked EGR valve or cooler; on common-rail TDI the EGR filter can block after a DPF regen with high soot load.

Volvo

EGR flow insufficient (D5 diesel).

Usual causes: soot-blocked EGR valve; blocked EGR cooler; sticking EGR valve

What the repair usually costs

CVT valve body replacement (remanufactured, in car)NZ$1,280–NZ$2,420 · A$1,200–A$2,400
Direct-injection petrol injectors (set)NZ$1,490–NZ$3,850 · A$1,350–A$3,520
Intake valve carbon clean (walnut blast, direct injection)NZ$530–NZ$1,190 · A$560–A$1,240
EGR valve replacement or cleanNZ$350–NZ$1,710 · A$330–A$1,630

Not sure what P0401 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.