While it might seem like a given that all modern cars have OBD2, the reality for JDM (Japanese Domestic Market) cars is a bit more nuanced. This article explores OBD2 compatibility in JDM cars, specifically focusing on a case study involving a 2004 Subaru Impreza WRX STi S401.
Using various diagnostic tools, including a generic OBD2 scanner, VAG cable with FreeSSM, Tactrix cable, and a Subaru SelectMonitor 2, tests were conducted on the S401. Surprisingly, even a basic $15 OBD2 scanner could read codes and OBD readiness using the K-line protocol, supporting monitoring for Oxygen sensors, O2 heaters, Fuel System, and Components. However, Catalyst and Evap monitoring were reported as “not supported.”
More advanced tools like FreeSSM and Tactrix provided comprehensive data access. Interestingly, the North American Subaru SelectMonitor 2, despite being designed for North American models, identified the S401 as a “2.0 Turbo” and “2002 ABS AWD MT.” Furthermore, all its functions appeared to operate correctly. This suggests a significant overlap in diagnostic protocols between JDM and North American Subaru models.
Even more surprising was the functionality of OBD Readiness checks. While Catalyst checks were “not supported,” the system reported this status rather than a failure or “not ready.” This nuance is crucial as a “not supported” status might be more lenient than a “fail” during emissions testing.
The S401, being a late-generation model, might possess broader OBD2 compatibility than its predecessors. The observed data and protocols mirrored those of a USDM (US Domestic Market) Subaru, with the primary differences being the unsupported readiness tests and the inclusion of turbo-related data.
Generic OBD2 scanners can often retrieve basic diagnostic information from JDM cars.
Surprisingly, a North American Subaru Select Monitor was able to correctly identify and communicate with the JDM S401.
More specialized tools like the Tactrix cable allow for in-depth data logging and diagnostics on JDM vehicles.
In conclusion, while there might be minor variations, many JDM cars, particularly later models, do support OBD2 protocols. The extent of this support can vary depending on the specific make, model, and year of the vehicle. However, as demonstrated by the S401 case study, even basic OBD2 scanners can often retrieve valuable diagnostic information. The “not supported” versus “fail” distinction for certain readiness tests is a critical detail for JDM car owners to understand, especially concerning emissions regulations.
