Abstract: A diagnostic method for a particulate filter in an exhaust line of an internal combustion engine is presented. The exhaust gas stream downstream of the particulate filter is monitored by a downstream soot sensor having a characteristic sensor cycle; and the accumulation of soot at an upstream soot sensor is monitored over a respective sensor cycle of the downstream soot sensor. The particulate filter operating status is decided on the basis of the information of the downstream and upstream soot sensors. The amount of accumulated soot is determined based on the sensor cycles of the upstream soot sensor, and may be expressed as a soot loading level or as a number of sensor cycles. The efficiency of the particulate filter may be determined from the respective number of sensor cycles of the soot sensors.