Abstract: An automotive system has a primary control module, such as an engine control module (ECM) configured for connection to a malfunction indicator lamp (MIL), and a secondary control module, such as a transmission control module (TCM), each in communication with each other over a bus. Each control module includes a respective diagnostic data status record. Each record includes a pending fault field, a confirmed fault field and an MIL control status field. An improved method for synchronizing the diagnostic data contained in the respective status records includes an extended status signal set that is used to communicate over the bus. The set includes a diagnostic testing complete signal, a fault present signal and a MIL request signal indicative of a request to illuminate the MIL. Logic in the receiving control module (ECM) interprets the extended status signal set to properly synchronize its diagnostic data status record with the TCM's, including both pending and confirmed faults.