For car enthusiasts and mechanics alike, understanding the nuances of automotive diagnostic systems is crucial. When it comes to older vehicles, particularly those from the 1990s, you’ll often encounter the terms OBD1 and OBD2. Knowing the Difference Between Obd1 And Obd2 Harness systems is essential for diagnostics, engine swaps, and performance tuning. While visually distinguishing between an OBD1 and OBD2 car might seem straightforward to some, identifying the harness type can be less obvious, especially in modified vehicles. This guide aims to provide a comprehensive breakdown of how to differentiate between OBD1 and OBD2 harnesses, ensuring you can confidently identify the system you’re dealing with.
One of the quickest initial indicators is the vehicle’s year. Generally, vehicles manufactured from 1996 onwards are OBD2, while those from 1995 and earlier are typically OBD1. Another simple check, as suggested by enthusiasts, involves locating the diagnostic port. OBD2 vehicles typically have a service port located near the cup holder or under the dashboard. However, these initial checks aren’t foolproof, particularly when dealing with engine swaps or modifications. For a definitive identification of your harness, a closer examination of specific components is necessary.
To accurately determine whether you have an OBD1 or OBD2 harness, especially in scenarios like engine swaps where the original setup might be altered, focus on the distributor plug. The distributor, often referred to as the “dizzy,” uses distinct plug types depending on the OBD generation. An OBD1 distributor harness will feature an oval-shaped plug with 8 wires connected to it. In contrast, an OBD2 distributor harness utilizes a square-shaped plug with only 4 wires. This difference in plug shape and wire count is a reliable visual cue for distinguishing between the two systems.
OBD1 Distributor Plug: Oval shape with 8 wires indicating an older system.
OBD2 Distributor Plug: Square shape with 4 wires characteristic of newer OBD2 systems.
OBD2 Distributor Plug Detail: Close-up view emphasizing the square shape and 4-wire configuration.
OBD2 Distributor Plug Angle: Another perspective of the OBD2 plug, highlighting its square design.
Visually comparing the two side-by-side further clarifies the difference. The oval OBD1 plug and the square OBD2 plug are distinctly shaped, making identification straightforward once you know what to look for.
OBD1 vs OBD2 Distributor Plugs: Side-by-side comparison showing the oval OBD1 plug on the left and square OBD2 plug on the right.
Another indicator, particularly useful in specific car models, involves an extra plug near the blue connector on OBD2 harnesses. If you are working on a vehicle that you suspect might have an OBD2 harness installed in an OBD1 car (like some 92-95 models), check for an unused plug near the large blue connector. OBD2 harnesses in certain models have an additional plug that is absent in OBD1 versions. The presence of this unconnected plug suggests an OBD2 harness is installed.
OBD2 Harness Extra Plug: Illustration of the blue plug and the additional unconnected plug unique to OBD2 harnesses in certain vehicles.
Moving to the distributor itself, the bolt holes used to mount the distributor to the cylinder head offer another point of differentiation. On an OBD2 distributor, the two top bolt holes are oval, while the bottom hole is a perfect circle. Conversely, an OBD1 distributor has oval bolt holes for all three mounting points. Examining the shape of these holes provides another visual method to distinguish between OBD1 and OBD2 distributors.
OBD1 Distributor Bolt Holes: All three bolt holes are oval, a characteristic of OBD1 distributors.
Further inspection of the distributor cap can reveal the presence of a sensor located directly under the rotor. OBD1 distributors often feature a sensor, which appears as a black box, positioned on top, just beneath the rotor. This sensor is typically absent in OBD2 distributors. Removing the distributor cap and checking for this sensor is another way to identify an OBD1 distributor.
OBD1 Distributor with Sensor: Black box sensor visible under the rotor, a feature of OBD1 distributors.
Another less visual, but tactile, method involves spinning the distributor’s internal piece that connects to the camshaft. An OBD1 distributor will produce a clicking sound with every slight rotation. An OBD2 distributor, however, will only click after rotating halfway. Additionally, OBD2 distributors are generally lighter than their OBD1 counterparts.
Lastly, the location of the Manifold Absolute Pressure (MAP) sensor differs between OBD1 and OBD2 systems in some vehicle models. In OBD1 vehicles (like certain 92-95 models), the MAP sensor is typically located on the firewall. In OBD2 vehicles (such as 96 and later models), the MAP sensor is usually found mounted on the throttle body. Checking the MAP sensor location can provide a quick confirmation, although this is model-dependent.
OBD2 MAP Sensor Location: MAP sensor mounted on the throttle body, typical of OBD2 systems in certain vehicles.
Why Convert to OBD1?
Many enthusiasts opt to convert from OBD2 to OBD1, particularly for performance tuning purposes. OBD1 systems are considered simpler and less stringent in their sensor requirements. OBD2 systems monitor a broader range of parameters, and even minor discrepancies can negatively impact engine performance. For those looking to tune their engines, OBD1 Engine Control Units (ECUs) are significantly more accessible. The tuning community has extensively “cracked the code” of OBD1 ECUs like P05, P06, P08, P28, and P72, making them readily tunable. Currently, OBD2 ECUs are considerably more challenging to tune due to their complex coding. Therefore, for individuals prioritizing engine tuning and modification, OBD1 systems remain the preferred, and often only viable, option.
In conclusion, distinguishing between OBD1 and OBD2 harnesses involves examining several key components and characteristics. From distributor plug shapes and wire counts to distributor bolt hole patterns and sensor locations, these visual and tactile cues will help you accurately identify the system you are working with. Understanding these differences between OBD1 and OBD2 harnesses is vital for anyone working on older vehicles, especially when dealing with modifications, diagnostics, or performance enhancements.
