The paper discusses the most frequently occurring types of damage in turbochargers fitted in modern combustion engines and their influence on the engine basic operational indexes. The following causes of turbocharger malfunctions have been discussed: no lubrication, low lubricant pressure, reduced lubricant quality, foreign objects in the charged air and in the exhaust gas. Example malfunctions resulting from the said causes have been shown. The experimental part discusses the influence of a reduction of the charging pressure resulting from a leakage in the intake system on the effective parameters of a diesel engine fitted in light-duty and heavy-duty vehicles. The leakage in the intake system has been simulated by boring holes of the diameter of 3 and 12 mm in the intake manifold downstream of the turbocharger. The influence has been determined of the leakage of the turbocharging system on the value of the charging pressure, maximum effective power, engine torque, unit and hourly fuel consumption and the concentration of the exhaust components. A significant impact has been observed of the leakage of the turbocharging system on the effective parameters of the tested diesel engine and exhaust gas composition.