Complex sentence: When the MIL is lit, the engine control unit stores a fault code related to the malfunction, which can be retrieved with a scan tool and used for further diagnosis, the diagnosis maybe retrieved without a scan tool in some car models.
Split into simpler sentences: When the MIL is lit, the engine control unit stores a fault code related to the malfunction, which can be retrieved with a scan tool and used for further diagnosis. The diagnosis may be retrieved without a scan tool in some car models.