P0400
Medium SeverityEGR Flow Malfunction
Emissions System
P0400 — Instant Answer
EGR Flow Malfunction
Severity: MEDIUM SEVERITY
Meaning: The EGR system flow is not within expected parameters.
Safe to drive? Usually yes with caution, but confirm root cause before long trips.
Estimated repair cost: $20 - $150
Most common causes:
- 1. Carbon-clogged EGR valve (35-45% of cases)
- 2. Stuck EGR valve (10-25% of cases)
- 3. EGR passage blocked (10-25% of cases)
Symptoms
- ⚠️Rough idle
- ⚠️Pinging under load
- ⚠️Failed emissions
- ⚠️Check engine light
Related Symptoms
Common Causes
How to Diagnose P0400
- 1Clean EGR valve and passages
- 2Test EGR valve operation
- 3Check vacuum lines to EGR
OEM Procedures for P0400
P0400 affects the EGR Valve. Found 8 OEM service manual procedures.
Adjustment/Replacement - Specification
Adjustment/Replacement - Specification
Adjustment/Replacement - Specification
Adjustment/Replacement - Specification
Adjustment/Replacement - Specification
Adjustment/Replacement - Specification
Adjustment/Replacement - Specification
Adjustment/Replacement - Specification
OEM Diagnostic Flowchart
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Parts & Tools for This Job
Common parts shoppers buy for P0400 EGR Flow Malfunction.
Oxygen Sensor
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Catalytic Converter
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EVAP Purge Valve
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Gas Cap
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OBD2 scanner
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Related Resources
Repair guides, symptom pages, and wiring diagrams related to P0400.
OEM Manual Evidence
Browse →EGR DTCS — 2013 Acura MDX 3.7L Eng VIN 2 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowledge Reimagined Home >> Acura >> 2013 >>...
EGR DTCS — 2013 Acura MDX 3.7L Eng VIN YD2 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowledge Reimagined Home >> Acura >> 2013...
Engine Control System - Advanced DTCS — 2013 Acura RDX 3.5L Eng VIN 3 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowledge Reimag...
Engine Control System DTCS — 2013 Acura RDX 3.5L Eng VIN 3 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowledge Reimagined Home >...
Related Symptoms
Browse →Rough idle often traces back to ignition, air metering, vacuum leaks, or timing-related faults before it becomes a full misfire complaint.
A check-engine light is a graph entry point into code pages, symptom-specific diagnosis, and the exact repair categories most often associated with those failures.
Exact Vehicle Hubs
Browse →Open the exact vehicle hub for a repair workflow commonly associated with P0400.
Open the exact vehicle hub for a repair workflow commonly associated with P0400.
Open the exact vehicle hub for a repair workflow commonly associated with P0400.
Open the exact vehicle hub grounded by OEM manual evidence related to P0400.
Open the exact vehicle hub grounded by OEM manual evidence related to P0400.
Open the exact vehicle hub grounded by OEM manual evidence related to P0400.
Exact Repair Workflows
Browse →Open the exact repair flow most commonly associated with P0400 on this vehicle.
Open the exact repair flow most commonly associated with P0400 on this vehicle.
Open the exact repair flow most commonly associated with P0400 on this vehicle.
Open the exact repair flow most commonly associated with P0400 on this vehicle.
Open the exact repair flow most commonly associated with P0400 on this vehicle.
Open the exact repair flow most commonly associated with P0400 on this vehicle.
Related Codes
The EGR is not flowing enough exhaust gas. Usually carbon buildup blocking the passages.
Too much exhaust gas is being recirculated, causing rough idle and stalling.
The EGR valve control solenoid or motor has a circuit fault.
Frequently Asked Questions
- What does EGR do?
- EGR recirculates exhaust gas back into the intake to lower combustion temperatures and reduce NOx emissions.
- Can I just remove the EGR?
- Removing EGR is illegal for road vehicles and will fail emissions. It can also cause engine knock due to higher combustion temps.
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Author & Review
Published by AllOEMManuals, founded by Lyndon Bedford, an automotive technician with 20 years of experience. He owned and operated a mechanic shop in Hurst, Texas from 2014 to 2022 and continues hands-on repair work.
Content may combine manual references, general repair templates, and AI-assisted drafting. Confirm the source, vehicle configuration, and applicability before working. Report corrections through our contact page.
Last updated: 2026-10-29