Connecting a modern OBD2 reader to an early Mazda with a 17-pin diagnostic connector can be challenging. This article explores the complexities of the Mazda 17-pin connector and its compatibility with the standard OBD2 interface.
Initial attempts to extract data from the 17-pin connector, such as monitoring the TEN, MEN, and FEN lines with an oscilloscope, yielded no discernible digital signals. This suggests that the Mazda system might require a specific “handshake” signal to activate communication. A test using a standard OBD2 reader wired according to a pinout diagram also failed to establish a connection.
Further investigation into the Miata community forums revealed that reverse-engineering efforts on the Mark 1 ECU didn’t find evidence of a standard RS232 serial communication protocol. This could indicate that Mazda employed a proprietary communication method, possibly to restrict diagnostic access to authorized dealerships. It’s speculated that they might have directly manipulated CPU pins for communication instead of utilizing the on-chip serial module.
The lack of readily available information and the potential use of a proprietary protocol pose significant obstacles to interfacing with the 17-pin connector. Even with a detailed pinout diagram, successful communication might require specialized hardware or software capable of emulating Mazda’s unique protocol.
One possible approach could involve emulating the Mark 1 ECU’s CPU in a virtual environment. By simulating the timing signals and running the original ROM, it might be possible to identify code sections related to diagnostics and decipher the communication protocol. However, this is a complex undertaking requiring significant technical expertise. For many owners of early Mazdas, investing in a vehicle with built-in OBD2 might be a more practical solution for accessing diagnostic information.
