On the present there is very intensively emphasized the environmental protection, which is also connected with reduction of emissions produced by the vehicles. The actual European emission standard EURO 6 will be replaced very soon with the new and even stricter standard EURO 7. There is a well-known fact that the new regulations are demanding with regard to the NOX emissions. However, there is at disposal a suitable technical solution, namely in the form of an innovative engine technology, which is called the HCCI. A principle of this technology consists in a self-ignition of the homogenous air-fuel mixture using the compression process. Combustion of the mixture is performed in the whole compression volume without a spark ignition, whereby the NOX emission level is almost negligible. However, this technology is also characterised by several serious problems, for example there is occurring a complication concerning control of the self-ignition phenomenon. The presented article introduces an original diagnostic system, which enables to control the whole self-ignition system and in this way to ensure a reliable operation of the HCCI engine. This system is patented now as well as it was tested in an experimental vehicle built for the international competition “shell eco marathon”