A system for detecting a leakage/failure in in an intake line of an internal combustion engine comprising an intake line (IL) and an exhaust line (EL), means (HFM) for measuring or for estimating a quantity of fresh air ({dot over (m)}HFM) entering said intake line (IL), means for measuring or for estimating a quantity of fuel ({dot over (m)}FUEL) injected in the engine (E), measurement or estimation means (λ and/or NOx), on the exhaust line, adapted to provide a first value (λmeasured) of an air/fuel ratio introduced in the internal combustion engine (E), the system comprising processing means (ECU) adapted to calculate a second value (λexp) of said air/fuel ratio, calculated on the basis of the measured and estimated quantities of fresh air ({dot over (m)}HFM) and fuel ({dot over (m)}FUEL) to calculate an error (λerr) between the first and the second value (λmeasured−λexp) and to detect a condition of leakage/failure if said error is outside a predefined interval [λerr−, λerr+] containing the value zero.