Let’s clear up the confusion around the diagnostic systems in 1994 and 1995 S-series Chevy and GMC trucks. Many owners find themselves scratching their heads when they see an OBD2-style connector under the dash, but their standard OBD2 scanner refuses to communicate. You’re not alone! This era of GM trucks is known for what some mechanics jokingly call “OBD1.5,” and understanding this system is key to diagnosing issues on your ride.
To appreciate the situation, let’s remember the older OBD1 systems. These systems, common in vehicles before the mid-90s, used an Assembly Line Diagnostic Link (ALDL) connector, often hidden under the dashboard. Retrieving diagnostic trouble codes (DTCs) from these systems was famously simple – sometimes just requiring a paper clip to bridge two pins!
Then came OBD2, a more advanced and standardized system mandated in the USA starting in 1996. OBD2 brought a standardized connector shape and communication protocols, requiring a scan tool to access the wealth of diagnostic information available.
However, the 1994 and 1995 model years for many GM vehicles, including the S10 and similar trucks, fall into a gray area. GM began transitioning towards OBD2, equipping these vehicles with the OBD2-style 16-pin Diagnostic Link Connector (DLC). Despite the OBD2 plug, these systems are not fully OBD2 compliant. A standard OBD2 scanner will likely fail to properly read the computer, leading to frustration and misdiagnosis.
Misinformation abounds. Some believe that if the Powertrain Control Module (PCM) is located under the hood, or if the distributor cap has horizontal wire terminals, it automatically signifies OBD2. These visual cues are not definitive for these specific model years.
For example, consider a 1995 GMC Jimmy with the “W” engine code and Central Port Injection (CPI). It features the PCM conveniently located under the hood,
and a distributor cap with horizontal wires,
and yes, the OBD2-style connector we’ve been discussing.
Yet, the underhood emissions sticker clearly states “OBD1 Certified.”
This “OBD1.5” system uses a blend of OBD1 and early OBD2 technologies. Crucially, it requires a specialized scanner to properly interface and retrieve diagnostic information. Owners have reported success with scanners like the Actron CP9150, specifically designed for these transitional GM years, or professional-grade scanners with appropriate software.
These systems often incorporate features like pre and post-catalyst oxygen sensors and crankshaft sensors, but may lack the full suite of OBD2 monitoring capabilities, such as comprehensive EVAP system monitoring. This is why some scanners might report “N/A” for certain OBD2 functions.
It’s also important to note that some 1994-95 S-series trucks, particularly those with Throttle Body Injection (TBI) engines and the older style air cleaner housings, may still utilize the true OBD1 ALDL system. Verification is always recommended.
The aim here is to consolidate knowledge and assist owners of these unique 94-95 GM trucks. If you’re wrestling with diagnosing your “95 S10 Obd2 Plug With Obd1” system, remember you’re dealing with a hybrid. Sharing your experiences and scanner recommendations can be invaluable to the community. Let’s build a helpful resource together!
