EGR in Trucks: Purpose, Operation & Common Failure Symptoms

A complete guide to Exhaust Gas Recirculation (EGR) systems in modern diesel trucks — how they work, why they affect emissions, and the common problems fleets experience under Euro 5–6 standards.

Engine Control Emission Systems
📅 Published on 2025-11-15 | ✍️ Semi Trailer News Engineering Desk

Image: EGR valve and piping assembly installed on a Euro 6 diesel engine

🔧 What Is the EGR System?

The Exhaust Gas Recirculation (EGR) system reduces **nitrogen oxide (NOx)** by recirculating a portion of exhaust gases back into the intake manifold. This lowers the oxygen concentration and combustion temperature, reducing NOx formation before combustion occurs.

⚙ How It Works

Modern Euro 6 trucks use an electronically controlled EGR valve. Depending on driving conditions, the ECU determines how much exhaust gas to recirculate.

• Low-load driving → higher EGR rate
• Heavy load or acceleration → low/no EGR
• Cold engine → EGR disabled to prevent condensation

🌡 EGR Cooler

To be effective, exhaust gases must be cooled. The **EGR cooler** reduces exhaust temperature from ~400°C to ~150°C before gases re-enter the intake, protecting the engine and improving NOx reduction efficiency.

⚠️ Common EGR Problems

• Carbon buildup inside the EGR valve
• EGR cooler leaks causing coolant loss
• Stuck-open or stuck-closed valves
• Excessive soot from injector/turbo problems

📉 Symptoms of a Faulty EGR System

• Limp mode / reduced engine power
• Engine knocking or rough idle
• Black smoke from exhaust
• Poor fuel economy
• DPF regeneration becoming more frequent

🔍 EGR vs SCR vs DPF

All three systems work together:

• EGR: Lowers NOx during combustion
• DPF: Captures soot
• SCR + AdBlue: Removes NOx after combustion

🧼 Maintenance & Cleaning

• EGR valve cleaning every 80,000–150,000 km
• Cooler inspection for internal leaks
• Using high-quality diesel to reduce soot
• Checking turbo and injector health

🏁 Final Thoughts

EGR is an essential part of modern emission control. Keeping it clean and functioning properly reduces fuel consumption, prevents DPF overload, and ensures Euro 5/6 compliance for fleet operations.

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