The OBD1.5 system, found in many early-to-mid 90s GM vehicles, bridges the gap between the older OBD1 and the modern OBD2 standards. This system uses OBD2 diagnostic trouble codes but transmits data using a faster 8192 baud rate, unlike the 160 baud rate of traditional OBD1. This article delves into the intricacies of the OBD1.5 system and how an OBD1.5 scan tool can unlock valuable diagnostic information. Understanding this unique system can be crucial for diagnosing and troubleshooting issues in these vehicles.
Decoding the OBD1.5 System
The Powertrain Control Module (PCM) in an OBD1.5 vehicle functions as a computer with a serial port. It transmits data through this port, allowing access to vital engine performance parameters. While the data isn’t as comprehensive as OBD2, it still offers more insights than standard OBD1. However, accessing this information requires a specific OBD1.5 scan tool and understanding of the communication protocol.
The key difference lies in the baud rate. The higher 8192 baud rate used by OBD1.5 demands a compatible interface. Many standard USB to serial converters won’t work due to this non-standard speed. Additionally, the PCM uses TTL level voltage (0-5V), while computers use RS-232 voltage (0-10V). This necessitates a level converter to ensure proper communication.
Hardware Requirements for OBD1.5 Scan Tools
Connecting to the OBD1.5 system requires specific hardware:
- Interface Cable: This cable connects to the diagnostic port, often located under the dashboard. It’s typically a 16-pin connector, sometimes referred to as the ‘Australian OBD1 connector’, which resembles an OBD2 connector but with a different pinout.
- Level Converter: This device converts the TTL voltage from the PCM to the RS-232 voltage required by the computer. A common solution is to use a MAX232 chip, which includes built-in capacitors for simplified implementation.
The circuit diagram below illustrates a typical setup using a MAX232 chip for level conversion:
Software Solutions for OBD1.5 Data Analysis
While various software options exist, one prominent solution for accessing OBD1.5 data is EFILive V4. This software provides live gauges and detailed diagnostic information. Although a paid software, a 30-day trial offers limited access to live data, allowing users to test its capabilities.
Conclusion: Choosing the Right OBD1.5 Scan Tool
Accessing the diagnostic data in your OBD1.5 GM vehicle requires a specific OBD1.5 scan tool capable of handling the unique 8192 baud rate and voltage levels. Understanding the hardware and software requirements is essential for successful data retrieval and analysis. While solutions like EFILive provide comprehensive functionality, other options may exist depending on your specific needs.
