Navigating the world of automotive diagnostics can be tricky, especially when you encounter systems that blur the lines. For owners of 1994 and 1995 GM S-series trucks, the On-Board Diagnostics (OBD) system is one such area of confusion. Often dubbed “OBD1.5,” this transitional system uses an OBD2 connector but doesn’t fully adhere to OBD2 standards. Let’s clear up the mystery surrounding the 95 S10 OBD2 plug that functions more like OBD1.
In older vehicles, particularly those with OBD1 systems, accessing diagnostic codes was straightforward. You could often use a simple paper clip to jump terminals in the Assembly Line Diagnostic Link (ALDL) connector, typically located under the dashboard.
With true OBD2 systems, a scan tool is essential to retrieve diagnostic trouble codes (DTCs) and access live data. However, the 1994-1995 GM trucks occupy a unique middle ground.
During this period, GM began implementing a more advanced diagnostic system across many vehicles. While these trucks feature the 16-pin OBD2 style connector, a standard OBD2 scanner will likely fail to communicate with the vehicle’s computer. This is where the term “OBD1.5” comes into play – it’s not quite OBD1, and definitely not fully OBD2.
Misconceptions abound regarding these systems. Some believe that if the Powertrain Control Module (PCM) is located on the coolant reservoir under the hood, it automatically signifies OBD2. Others point to distributor caps with horizontal wires as an indicator of OBD2. These assumptions are often inaccurate.
To truly understand these systems, we need to focus on facts and shared experiences. Personal anecdotes can be invaluable in building a reliable knowledge base for owners of these unique vehicles.
For my own 1995 GMC Jimmy, diagnosing issues required a specific scanner designed for 1994-1995 GM models. I discovered the Actron CP9150 on eBay for around $250, which proved to be compatible. Professional-grade scanners like those from Snap-on, equipped with the appropriate software, can also effectively diagnose these systems.
It’s important to note the configuration of my truck, which may be representative of others from this period. My Jimmy, equipped with the “W” engine code and Central Port Injection (CPI), features the PCM located under the hood:
It also has a distributor cap with horizontal wires, a feature sometimes mistakenly associated with OBD2:
Crucially, it uses the OBD2 style 16-pin Diagnostic Link Connector (DLC):
Despite these seemingly OBD2 characteristics, the Vehicle Emission Control Information (VECI) sticker under the hood explicitly states “OBD1 Certified”:
The definitive test, in my experience, is scanner compatibility. If a standard OBD2 scanner fails to read the system, it should not be considered OBD2 compliant, regardless of the connector type.
My 95 Jimmy is equipped with a pre-catalytic converter oxygen sensor and a post-catalytic converter oxygen sensor, along with a crankshaft position sensor. Interestingly, my scanner indicated “N/A” for EVAP monitoring, suggesting that Evaporative Emission Control system monitoring was not yet fully implemented or accessible in the diagnostic protocol at that time.
It’s also worth considering that during these model years, some trucks were equipped with Throttle Body Injection (TBI) engines. These engines, characterized by a vertical throttle body and a traditional air cleaner assembly, are believed to have retained the older OBD1 ALDL system. Confirmation or correction on this point would be valuable for a comprehensive understanding.
Ultimately, the goal is to consolidate our collective knowledge and provide practical guidance for individuals who own these 1994-1995 GM trucks and are grappling with their unique OBD systems. Sharing verified information is crucial to demystifying the “95 S10 Obd2 Plug With Obd1” conundrum and ensuring effective vehicle diagnostics and maintenance.
