A method and device for diagnosing a low pressure exhaust gas recirculation system (LPEGRS) of an internal combustion engine having an intake area for supplying fresh air which includes in succession in the flow direction a first section having a low pressure in which an air mass flow sensor is situated, a compressor and a second section having a high pressure, the engine exhaust area including a second section having a low exhaust gas pressure, and the LPEGRS which has an adjustable LPEGR valve recirculating at least a portion of the exhaust gas in the second section of the exhaust area to the first section of the intake area. The fresh air mass flow taken in is measured by the air mass flow sensor, the total mass flow flowing through the compressor being ascertained, the LPEGR mass flow being ascertained from the difference between the total mass flow and the fresh air mass flow taken in, an estimated value being calculated for the LPEGR mass flow, the difference between the ascertained LPEGR mass flow and the estimated value being formed, and an error signal being output for a deviation. The procedure is for detecting exhaust gas-relevant errors.