A METHOD OF DIAGNOSING AN ENGINE SYSTEM

The present invention relates to a method of diagnosing an engine system (10) comprising an engine (15) and an exhaust aftertreatment system (20) for reducing emissions of the exhaust gases from the engine. The engine system comprises a plurality of replaceable engine system components (12). The method comprises maintaining (S10) a database (18) with component data, the component data comprising, for each one of the replaceable engine system components, a deterioration efficiency parameter (ηD1 - ηDn) correlating the deterioration status (DS) of the replaceable engine system component to emission reducing efficiency (ηE), and a utility component parameter (UC1 - UCn) comprising component exchangeability data (CE1 - CEn); determining (S20) the deterioration status (DS1 - DSn) of each one of the replaceable engine system components; estimating (S30) the emission reducing efficiency (ηE1 - ηEn) for each one of the replaceable engine system components in response to the determined deterioration status and the deterioration efficiency parameter; based on known relation between component exchangeability data and the resulting emission reducing efficiency of a potential exchange of the replaceable engine system component, identifying (S40) a replaceable engine system component to exchange.