The reduction of greenhouse gas is becoming increasingly important for humankind, and vehicles with low CO₂ emissions have a part to play in any reduction initiatives. Diesel engines emit 30% less CO₂ than gasoline engines, so diesel engines will make an important contribution to the overall decrease. Unfortunately diesel exhaust gas contains particulate matter (PM) which may cause health problems, and such PM emissions are regulated by law. In order to reduce PM, especially soot, diesel particulate filters (DPFs) are widely fitted to diesel vehicles. A DPF can remove more than 99% by weight of soot from exhaust gas under normal operating conditions, and they are one of the most important methods to achieve any regulation targets. But if the system malfunctions, the PM emissions may exceed the regulation limit. To detect such PM leakage, on-board diagnostics (OBD) are required.In the real world vehicles are used in a variety of different driving situations and the total amount of PM relates to both the PM concentration and operating time, for example, urban driving with long journey times, and short bursts of high speed driving, both have an important impact on our environment. An OBD needs to perform at not only higher soot concentrations but also at lower soot concentrations.Therefore, a new direct detection sensor, mainly made of ceramic materials has been developed to detect lower soot concentrations. Particulate collecting electrodes, sensing electrodes and heaters are all built-in and have been designed to give highly effective collecting and sensing of the amount of soot in exhaust gas. As the sensing method is less influenced by particulate conductivity, this sensor can detect lower soot concentrations in the New European Driving Cycle (NEDC) mode and the Federal Test Procedure (FTP) mode.