A particulate matter sensor includes a first pair of sensing electrodes with a gap therebetween and a second pair of sensing electrodes with a gap therebetween. A method for determining an amount of soot on the particulate matter sensor includes determining the electrical resistance between the first pair of electrodes and the electrical resistance between the second pair of electrodes. The amount of soot deposited on the particulate matter sensor is determined based on the electrical resistance values. The time rate of change of resistance between the first pair of electrodes and the time rate of change of resistance between the second pair of electrodes are determined. The first and second rates of change are compared to each other and to threshold values, and the determination of soot amount may be modified depending on the results of these comparisons.