Other P0400-P0408 codes may be set due to an inoperative EGR valve, sensor or possible wiring fault. These are likely quicker/easier to fix but may result in no EGR function.

Vacuum-operated EGR valves use a vacuum solenoid to vary the vacuum and direct it, opening and closing the EGR. Some systems even have sensors that feed information to the onboard computer. Digital ...

Volvo confirms flow with a downstream pressure sensor. The net result? "We get exactly the amount of cooled EGR we need — no more, no less — which improved fuel economy while meeting emissions," ...

Nicolò Cavina, Carlo Siviero, Rosanna Suglia, Residual Gas Fraction Estimation: Application to a GDI Engine with Variable Valve Timing and EGR, SAE Transactions, Vol. 113, Section 4: JOURNAL OF FUELS ...