Thank you for your reply. I looked at C_UDMI it seems like it doesn't access the field variables directly by itself as there are calculated by the model it only stores variables in the allocated "user-defined memory" which are retrieved by cell field variable macros (e.g. C_UDMI() = C_T() would store the cell temperatures retrieved by C_T() in the allocated memory using C_UDMI() but doesn't retrieve the temperatures by itself) and once this data it stored in memory it can than be accessed using C_UDMI() for other purposes. It only links cell field variable macros with the allocated memory. I'm looking for a cell field variable macros similar to C_T(), C_U(), C_P() but for concentration. The closest thing I found was C_UDSI but this is used with UDS transport equations but in my case I don't need to define UDS transport equations since the species model is sufficiate for my problem. Can I somehow maybe pass the species model in the argument of C_UDSI(c,t,i) (e.g. using the species model index if it has one or something)?. Please help!!