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OBD code information sheet

https://dvireports.com/p0400

Fault codes DVI Reports
P0400

EGR A Flow

Safe to keep driving?Caution / Repair soonArrange diagnosis soon

Arrange diagnosis soon. A limited journey may be reasonable only if the vehicle runs normally without red warnings, abnormal temperature or severe loss of power. Stop safely if serious symptoms develop.

LowCautionCritical
System groupEmissions & exhaustEGRRepair costs

Technical explanation

EGR A Flow. Basic catalogue definition; diagnostic details have not yet been reviewed.

Symptoms

  • Rough idle, reduced power or higher emissions.

Possible causes

Possible causes to investigate, not a statistical ranking or a parts-replacement list.

  1. Sticking EGR valve, blocked passages or damaged vacuum hoses.

Step-by-step diagnosis

Checks

Work through the steps before replacing parts. Adapt the checks to the manufacturer’s procedure.

  1. Inspect EGR passages, hoses and connections; test position sensor.

Components to check

This list does not confirm failed components and is not a replacement recommendation. Verify the fault cause and vehicle applicability first.

  • Inspect: EGR valve, position sensor, hoses and passages.

Check the fuses before ordering a part

An OBD code describes a detected condition; it does not tell you which part to replace. Start with the fuse for the affected circuit.

Find the fuse for your vehicleChoose the make and model, then look up the fuse position in the catalogue.

If the fuse is good, carry on like this:

  1. Check the relevant supplies and connectionsWhere the diagnostic procedure calls for electrical checks, verify supply, ground and connectors under the manufacturer’s activation conditions.
  2. Run the specified component testUse the manufacturer’s test for this code and component before deciding it has failed.
  3. Order only after the fault is demonstratedReplace a part only when the prescribed tests identify it as defective.
Check details
  • Identify the circuit and any relevant fuse: Confirm the vehicle, engine, code meaning and stored operating conditions first. A fuse link is a location aid, not evidence that the fuse caused this code. Use the specified type and rating; do not repeatedly replace a fuse that opens.
  • Check the relevant supplies and connections: Use the specified engine state, circuit conditions and expected values. Have live measurements performed by someone qualified. For non-electrical faults, follow the relevant mechanical, fluid, pressure or leak checks instead.
  • Run the specified component test: Do not apply a generic resistance range. Any resistance or continuity test requires a de-energized circuit and an isolated component, with the correct pins and temperature from the procedure. Some components need a different kind of test.
  • Order only after the fault is demonstrated: If results are normal, continue the relevant wiring, control, mechanical or intermittent diagnosis. Check for related faults and verify the repair under the required conditions. A code or a completed checklist alone does not justify replacement.
Fluke · Continuity testing

If the procedure involves airbag/SRS, pretensioners or a high-voltage system, stop DIY testing and use qualified service. Do not probe these circuits with a multimeter.

Fuses to check for this code

P0400 · Associations from the imported catalog

Confirm the model, year and engine. Associations come from the imported catalog; a code alone does not prove a blown fuse. Check machine-translated descriptions against the vehicle manual. Use the exact rating specified by the manufacturer when replacing a fuse.

256 / 256 associations found

  • Alfa

    Alfa Romeo 145 1994 2000

    815 A
    Box / group
    Assignment of fuses in the passenger compartment (type 1)
    Circuit / component
    1) Instrument cluster, Windscreen-headlamp washer pump, Reversing lights, Airbag, Wing mirror adjustment, Clock, Check panel, Alfa Romeo Code system, EGR
    View fuse 8 in the table

  • Alfa

    Alfa Romeo 146 1994 2000

    815 A
    Box / group
    Assignment of fuses in the passenger compartment (type 1)
    Circuit / component
    1) Instrument cluster, Windscreen-headlamp washer pump, Reversing lights, Airbag, Wing mirror adjustment, Clock, Check panel, Alfa Romeo Code system, EGR
    View fuse 8 in the table

  • BMW

    BMW 2 Series Active Tourer And Gran Tourer F45 F46 2014 2021

    0620 A
    Box / group
    B38 – 1.5L (216i, 218i, 225xe)
    Circuit / component
    Diesel:EGR Cooler Bypass Flap Changeover Valve, Nitrogen Oxide Sensor before SCR Catalytic Converter
    View fuse 06 in the table

  • BMW

    BMW 2 Series Active Tourer And Gran Tourer F45 F46 2014 2021

    0220 A
    Box / group
    Power Distribution Box (Diesel 1.5 & 2.0L)
    Circuit / component
    Oil Level Sensor, Oxygen Sensor after Catalytic Converter, EGR Cooler Bypass Flap Changeover Valve, Oxygen Sensor before Catalytic Converter, Changeover Valve – Compressor Bypass Plate (2.0L B47)
    View fuse 02 in the table

  • BMW

    BMW X1 F48 F49 2015 2022

    0620 A
    Box / group
    Integrated Supply Module (Diesel)
    Circuit / component
    EGR Cooler Bypass Flap Changeover Valve, Nitrogen Oxide Sensor before SCR Catalytic Converter
    View fuse 06 in the table

5 / 256 associations shown

Find another model in the fuse catalog →

Vehicle experiences and cases

User-reported cases published after moderation. Approval does not verify the diagnosis; the same code can have different causes.

No experiences have been published for this definition yet. You can be the first to share the checks and outcome.

See all vehicle experiences

Manuals, components and vehicle guides

Find the relevant procedure in the workshop manual for your vehicle. A fault code alone does not identify a failed part, powertrain or exact schematic.

Find workshop manual / diagramComponents to checkRelated issues and checks

Manuals open at their original source. Exact diagram availability depends on the build year, engine and manufacturer access.

Can I fix it myself?

Once the cause is confirmed, open the job sheet: difficulty, time, tools, parts and steps. Common jobs for P0400:

Clean or replace EGR valve →

How to fix P0400: step-by-step guide

Symptoms, causes, visual inspection, scan-tool or multimeter tests, replacement and clearing the code, with safety warnings.

EGR valve cleaning: symptoms, causes and step-by-step procedure →

Exhaust-gas recirculation

General system guidance · not a confirmed diagnosis

Flow control uses different sensors and actuators across vehicles. Confirm the definition for the installed architecture.

The association is based on the imported description. This information explains the system; it does not confirm a procedure for the exact code, model or engine. Verify applicability in manufacturer documentation.

Checks for this type of system

  1. Compare EGR request with measured response.
  2. Check restrictions, connectors and hoses only where fitted.

Useful diagnostic data, where available

  • EGR position or estimated flow.
  • Air mass and pressure during permitted testing.

Normal values and thresholds vary by vehicle and are not assumed here.

Mistakes to avoid

  • Not every EGR system is vacuum controlled.
  • Cleaning cannot automatically repair an electrical fault.
System-guide sources

References support general principles, not individual verification of every associated code.

Continue your research

Links to related systems, warning lights and vehicle examples.

EGR valve cleaning: symptoms, causes and step-by-step procedureCheck Engine light: meaning and urgencyWhat is EGR?What is a DPF?Read the code with an OBD scanner

Similar codes

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Exhaust gas recirculation flow insufficient

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P0402Caution / Repair soon

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P0403Caution / Repair soon

General code

EGR A Control Circuit/Open

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Open sheet
Report a problem

What should be corrected in this sheet? Do not include names, phone numbers, registration plates or VINs.

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