For owners of the 1990 Lexus LS400, known in Japan as the Toyota Celsior, finding a compatible diagnostic scanner can present unique challenges. Unlike US and European vehicles of the same era, this JDM (Japanese Domestic Market) classic doesn’t adhere to the standard OBD2 protocol. Instead, it utilizes J-OBD or M-OBD protocols, sometimes referred to as the Toyota S2000 protocol, creating a hurdle for modern diagnostic tools.
Many owners, in their quest to decipher check engine lights and troubleshoot issues, turn to readily available OBD2 scanners and smartphone applications. One such app, Torque Pro, has been mentioned in online forums as potentially working with JDM vehicles, with users suggesting the addition of specific protocols. However, as one owner discovered while attempting to diagnose their Celsior, this method isn’t universally effective.
Facing similar difficulties, some owners have resorted to the traditional TCCS (Toyota Computer Controlled System) method. This onboard diagnostic approach involves bridging terminals Tc and E1 in the engine bay’s diagnostic port. While this method can retrieve fault codes, such as code 21 in one instance, these codes often translate to multiple generic OBD2 codes. In the case of code 21, it corresponded to OBD2 codes P0130, P0135, and P0141, all pointing towards potential issues with the oxygen sensors.
Interestingly, further investigation revealed anecdotal evidence suggesting that OBD2 code P0135, typically associated with an O2 sensor heater circuit malfunction, might be triggered by a faulty Coolant Temperature Sensor in these specific models. This highlights the nuances of interpreting generic OBD2 codes on JDM vehicles.
Experiences with professional diagnostic tools from local garages and ECU specialists have been largely unsuccessful in establishing a connection with the ECU of the 1990 Celsior. This reinforces the notion that standard OBD2 equipment often falls short when dealing with these early JDM systems.
However, a glimmer of hope appears with Toyota TIS Techstream, Toyota’s proprietary diagnostic software. Online forum discussions suggest that Techstream might successfully connect to a JDM Celsior if the software’s region is set to “Japan” and the specific JDM 1UZ-FE engine is manually selected. Verification from users with hands-on experience with Techstream on a 1990 Celsior would be invaluable in confirming this potential solution for diagnosing these iconic vehicles and resolving issues like persistent CEL illumination, rough idling, and driveability concerns.
