1) What is the EGR system and why it exists

The EGR (Exhaust Gas Recirculation) system routes a controlled amount of exhaust gas back into the intake to
reduce combustion temperature and lower NOx emissions.
In gasoline engines it dilutes the charge; in diesel engines it reduces oxygen concentration. Benefits come with trade-offs:
more intake deposits over time and small reduction in volumetric efficiency.

2) Typical faults and symptoms

• Carbon build-up and oil vapour clogging the valve or cooler;
• Vacuum circuit or electric actuator not allowing full closure/opening;
• Leaking valve → unmetered air, unstable idle, smoke on tip-in;
• Position/flow plausibility and temperature sensor faults;
• Frequent MIL/DTC: “EGR flow insufficient/excessive”, “EGR stuck open”.

3) Diagnostic checklist

• Read/record all DTCs and live data before any change;
• Compare commanded vs actual EGR, plus MAF/MAP/EGT at idle and part load;
• Check vacuum lines/solenoids or connector (depending on actuation type);
• Cooler integrity (no coolant loss), manifold joints and deposits;
• Ensure ECU base software is updated prior to calibration.

4) Software EGR Off + Mandatory Mechanical Blanking

A) Software (ECU calibration)

Deactivate EGR requests, related maps and plausibility checks while keeping diagnostics coherent (no blanket DTC removal).
Validate the air model so MAF/MAP remain consistent and idle stays stable.
Software alone does not guarantee physical sealing.

B) Mechanical blanking — always required

Install a solid blanking plate (no hole) even if the valve appears functional.
Why it’s mandatory:

• Valves frequently do not seal 100% (wear, deposits, lash) → residual flow persists;
• Prevents passive breathing and backflow; stabilizes MAF and intake pressure;
• Ensures long-term reliability and clean intake when paired with proper software EGR Off.

Conclusion: Plate + Software is the only professional combo. Software-only deletes are not recommended.

5) Step-by-step EGR Off procedure

1. Read & back up the ORI (OBD / Bench / Boot). Record SW/HW IDs.
2. Install the blanking plate (solid, correct location) and reassemble with new gaskets if needed.
3. Apply a verified EGR Off calibration: duty/request 0%, switches/logics off, plausibility coherently managed.
4. Deactivate only EGR-related DTCs (flow/position/plausibility). Keep the rest intact.
5. Fix checksum and flash with stable voltage (12–14 V, ≥50 A).
6. Reset adaptations (idle/air model where supported) and clear residual DTCs.
7. Road test & logging: idle → part-load → cruise → brief WOT; verify MAF/MAP/EGT consistency and no smoke.

6) Post-tuning checks

• Stable idle, trims within normal range; no oscillations;
• No MIL; no EGR-flow plausibility or related DTCs;
• Smooth MAF/MAP behaviour on tip-in and lift-off;
• Coolant level stable (if cooler was suspected);
• DPF/SCR systems remain coherent where present.

7) Quick FAQ

Do I always need a blanking plate?

Yes. Even a healthy valve may not seal perfectly. The plate guarantees full isolation and a stable air model.

Can I do software only?

Not recommended. Without mechanical sealing, residual flow can cause smoke, rough idle or plausibility issues.

Does EGR Off always improve power?

It improves consistency and reduces fouling. Power gains depend on engine/tune and are not guaranteed.

Can I just unplug the EGR connector?

No. You will trigger DTCs and limp mode. Use proper calibration + blanking.