P0400

Exhaust Gas Recirculation Flow Malfunction

OBD-II diagnostic trouble code P0400indicates a fault detected by the vehicle's onboard computer. This code applies to all OBD-II compliant vehicles and should be addressed promptly to avoid potential engine or emissions system damage.

Severity Level 3 — Moderate

This code indicates a moderate issue that may affect vehicle performance and fuel economy. Continued driving is possible in most cases, but prompt diagnosis and repair are recommended to prevent further damage.

Common Symptoms

• Check Engine Light on
• Engine pinging/detonation under load
• Rough idle or stalling
• Failed emissions test (high NOx)
• Surging at steady highway speeds

Possible Causes

• Clogged EGR passages in intake — carbon deposits restrict flow, very common on direct-injection engines
• Faulty EGR valve — stuck open (causes rough idle) or stuck closed (causes knocking)
• Faulty EGR vacuum solenoid or control circuit
• Cracked or disconnected vacuum lines to EGR system
• Faulty DPFE sensor (Ford vehicles)
• Clogged EGR tube between exhaust manifold and EGR valve

Common Fixes

• Clean EGR passages and intake manifold runners ($200-500 labor)
• Replace EGR valve ($150-450)
• Replace EGR vacuum solenoid ($40-150)
• Replace cracked vacuum lines ($5-30 DIY)
• Replace DPFE sensor ($40-100)

Estimated Repair Cost

These are estimated costs based on generic repair data. Actual costs may vary depending on your vehicle, location, and labor rates.

Explore Repair Costs

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