Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Garage soon

P0401 on Citroën: causes and affected engines

P0401 means: exhaust gas recirculation (EGR): insufficient flow detected.^[1][2][3] Citroën has 5 documented faults that can trigger it, across 4 engines: 1.6 HDi, 2.0 HDi, 1.4 HDi and 2.0 BlueHDi. Only a diagnosis can confirm the cause on your car.

Documented faults

that can trigger it

Engines

used by Citroën, with at least one of them

Citroën models

with at least one of these faults

Urgency

Garage soon

Reviewed on 2 October 20267 sources How we work

Documented faults in Citroën engines that can trigger P0401

Grouped by engine or model, from most to least important. These are faults with the EGR valve and with carbon build-up in the intake: not all of them will necessarily set the code, and only a diagnosis confirms the cause on your car.

1.6 HDi

In Berlingo II, C-Elysée, C3 I, C3 II, C3 Picasso, C4 I and 6 more models

2.0 HDi

In Berlingo II, C4 Picasso I and C5 II

- Medium severityFrequency: CommonEmissions controlEGR valve blocked by sootThe 2.0 HDi's EGR valve gets coated in soot and sticks, especially on the 107/120 and 136/138 hp versions; it causes jerking, limp mode and the engine warning light, although it can usually be solved by cleaning it.Repair (garage): €200–€350

1.4 HDi

In C1 I, C2, C3 I and C3 II

- Medium severityFrequency: OccasionalEmissions controlEGR valve clogged with carbonThe EGR valve, which recirculates part of the exhaust gases to reduce emissions, can seize or clog up with the carbon those gases carry. It appears in a noticeable minority of the reports collected for the 68 hp version.

2.0 BlueHDi

In C4 Picasso II, C5 Aircross and Jumpy III

- Medium severityFrequency: OccasionalEmissions controlEGR valve blocked by carbon depositsThe EGR valve on the 2.0 BlueHDi can get clogged with carbon deposits and stick, causing juddering and limp mode. Specialists place the greatest risk in the earlier 120 and 136/138 hp versions without AdBlue; at 150-180 hp the documented cases are in the minority.Repair (garage): €200–€350

Common causes of P0401 on any make

From most to least likely, according to the sources.

1Carbon and soot blocking the EGR valve, its passages or the recirculation pipe: Carista names it as the most common cause and Samarins counts it among the most frequent problems.^{[1][2][4][5][6]}
2EGR valve stuck closed, failing to open or not opening far enough, or simply faulty.^{[1][2][4][5][6]}
3Lack of vacuum in pneumatically operated valves: cracked or badly connected hoses, or a faulty vacuum solenoid.^[1][2][4][5]
4Faulty EGR position sensor, or an EGR temperature sensor covered in carbon; on some Fords, also the DPFE differential pressure sensor.^[1][2][4]

What to check first

The first diagnostic steps, from the most likely and cheapest to check to the most expensive.

1Start with the simplest things: vacuum hoses (if the EGR is pneumatic), and the valve's wiring and connectors. Repair anything damaged before removing anything.^[1][4][6]
2With a diagnostic tool, command the EGR valve open: the engine should run roughly or even stall. If it does not react, the gas passage is blocked or the valve is not working.^[4]
3Remove the valve and check for carbon; also clean the EGR passages in the intake manifold. When soot is the cause, cleaning is usually enough.^[2][4][5]

Full guide to P0401: symptoms, diagnosis and whether you can drive

Frequently asked questions

Which Citroën engines have faults that can trigger P0401?

1.6 HDi (2 faults), 2.0 HDi (1 fault), 1.4 HDi (1 fault) and 2.0 BlueHDi (1 fault). Each fault has its own page with the affected years and versions, the symptoms and the repair cost.

What does code P0401 mean on a Citroën?

Exhaust gas recirculation (EGR): insufficient flow detected. The ECU has found that the EGR valve is returning less exhaust gas to the intake than it has been asked for: just when the commanded flow should be passing, the recirculated flow falls short. It is the opposite of P0402, where too much gas is recirculated. It is a generic OBD-II code: it means the same on a Citroën as on any other make.^[1][2][3][5]

Can I keep driving with P0401?

Garage soon. You can normally get to a garage, but it is best to repair it soon. Autodoc does not believe it causes very serious problems in the short term, although it does not recommend carrying on driving as normal while the symptoms persist and asks for a repair as soon as possible to avoid greater damage; Carista rates it as medium severity. With less EGR, combustion temperature rises and, according to TAT, so does NOx; Carista lists knocking under load among the symptoms. Diariomotor adds that leaving a blocked EGR for a long time could affect the injectors, the intake manifold or the particulate filter.^[1][2][3][7]

Sources

Every fact on this page links to its source. If you find an error, let us know.

Código OBD2 P0401: causas, síntomas y cómo corregirloAutodoc Club · Technical documentation · consulted 2 October 2026 · in Spanish
P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient DetectedCarista · Technical documentation · consulted 2 October 2026
P0401: Exhaust Gas Recirculation Flow Insufficient DetectedThe Automotive Technician (TaT) · Technical documentation · consulted 2 October 2026
OBD II code P0401 Exhaust EGR Flow InsufficientSamarins.com · Technical documentation · published 25 July 2021 · consulted 2 October 2026
OBD-SystemMS Motorservice (Pierburg) · Manufacturer · consulted 2 October 2026
Fault Code 16785/P0401/001025Ross-Tech Wiki · Technical documentation · consulted 2 October 2026
Síntomas de que la EGR de tu coche diésel está obstruidaDiariomotor · Motoring press · published 1 March 2020 · consulted 2 October 2026 · in Spanish