P0400
Medium SeverityEGR Flow Malfunction
Emissions System
What Does P0400 Mean?
The EGR system flow is not within expected parameters.
Common Fix
Clean or replace EGR valve
Estimated Cost (DIY)
$20 - $150
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 Diagnostic Flowchart
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Related Resources
Repair guides, symptom pages, and wiring diagrams related to P0400.
OEM Manual Evidence
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A L L Diagnostic Trouble Codes ( DTC ) — 2013 Chevy Truck Express 2500 V8-6.6L DSL Turbo Service Manual | Operation CHARM Operation CHARM :...
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 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.
Exact Repair Workflows
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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.
Related Repair Guides
If your vehicle has triggered P0400, these DIY repair guides may help: