The ISO 9141-2 protocol plays a crucial role in OBD2 (On-Board Diagnostics II) communication, particularly for vehicles utilizing the K-line for diagnostic data transfer. While the concept of leveraging ISO 9141-2 to extract and replicate engine control unit (ECU) maps for tuning purposes is intriguing, it’s essential to understand the practical limitations and technical nuances of this diagnostic standard.
One proposed application involves using ISO 9141-2 to “clone” original ignition and injection maps from a stock ECU. The idea is to operate a system in a learning mode, reading parameters via the K-line and populating corresponding map fields. Although conceptually simple, the inherent speed constraints of K-line diagnostics pose a significant challenge.
The OBD2 specification dictates a minimum 100ms delay between messages on the K-line. This latency restricts the data acquisition rate, limiting the number of Parameter IDs (PIDs) that can be effectively sampled per second. Ideally, this allows for approximately 8.5 PIDs per second. However, real-world implementations often fall short of this theoretical maximum. Using a Windows-based system with a Virtual Com Port can reduce the rate to around 6 PIDs per second. Furthermore, Bluetooth dongles, commonly used for wireless OBD2 connectivity, can further decrease the sampling rate to approximately 4 PIDs per second. These slower rates become problematic, especially during dynamic engine operation such as hard acceleration, where parameter readings can become significantly desynchronized and less representative of the actual engine state.
Beyond speed limitations, the standard OBD2 protocol has constraints in the range of data it exposes. Notably, injector pulse width (PW), a critical parameter for fuel mapping, is not typically a standard OBD2 output. To access more comprehensive and faster diagnostic data, many vehicle manufacturers implement proprietary protocols alongside the standard OBD2. These proprietary systems offer enhanced diagnostic capabilities beyond the scope of ISO 9141-2 and standard OBD2 PIDs. Moreover, attempting to reconstruct ECU maps through OBD2 is further complicated by the intricate nature of modern OEM ECUs. These units often employ a multitude of maps, not just single ignition and injection maps. Therefore, any attempt to “clone” a map via ISO 9141-2 would likely result in an averaged representation, rather than a precise duplication of any single original map.
In conclusion, while ISO 9141-2 provides a standardized method for accessing vehicle diagnostic data, its inherent limitations in speed and data availability make it less than ideal for tasks like high-resolution ECU map cloning. For advanced diagnostics and comprehensive data acquisition, exploring faster communication protocols and proprietary manufacturer-specific interfaces is often necessary.
