Understanding the difference between OBD1 and OBD2 systems in Honda vehicles is crucial for diagnostics, modifications, and tuning. While visually similar at first glance, these systems have significant underlying differences. This guide provides a detailed comparison to help you easily distinguish between OBD1 and OBD2 in your Honda.
One of the quickest ways to initially identify your Honda’s OBD system is by checking the model year. Generally, Honda models from 1992 to 1995 utilize OBD1, while models from 1996 and onwards are equipped with OBD2. Another preliminary check involves looking for the diagnostic service port. OBD2 Hondas typically have a service port located near the cup holder. However, for a definitive identification, especially if your car has undergone modifications or engine swaps, a more detailed inspection is necessary. Let’s delve into the specific visual and technical differences between OBD1 and OBD2 Honda systems.
Key Differences Between OBD1 and OBD2 Honda
To accurately differentiate between OBD1 and OBD2 harnesses and components in your Honda, focus on these key areas:
1. Distributor Plugs
The distributor plug, or ‘dizzy’ plug, is a significant visual differentiator.
OBD1 Distributor Plug: Features an oval shape with 8 wires connected to it.
OBD2 Distributor Plug: Features a square shape with only 4 wires.
Image: An OBD1 distributor plug, clearly showing its oval shape and the presence of 8 wires.
Image: An OBD2 distributor plug, highlighting its square shape and the reduced number of 4 wires.
Image: Two OBD2 distributor plugs shown from different angles to further illustrate the square design.
Image: A side-by-side comparison of OBD1 (left) and OBD2 (right) distributor plugs, emphasizing the oval vs. square shape and wire count difference.
2. Wiring Harness Plugs (Specifically for Preludes)
For Honda Preludes, there’s an additional harness plug difference to note. If you are inspecting a 92-95 (OBD1) Prelude and find an unplugged connector near the large blue plug on the harness, it indicates an OBD2 harness might have been used. OBD2 Preludes have an extra plug by the blue plug that is absent in OBD1 models.
Image: The blue plug area on an OBD2 Prelude wiring harness, pointing out the additional extra plug that is not found on OBD1 harnesses.
3. Distributor Bolt Holes
The bolt holes on the distributor where it mounts to the cylinder head also differ.
OBD2 Distributor Bolt Holes: The two top bolt holes are oval, while the bottom hole is a perfect circle.
OBD1 Distributor Bolt Holes: All three bolt holes are oval.
Image: An OBD1 distributor highlighting that all three bolt holes used for mounting are oval in shape.
4. Distributor Sensor (Under the Distributor Cap)
Another internal difference lies under the distributor cap.
OBD2 Distributor Sensor: OBD2 distributors feature a sensor located on the top, right under the rotor, which appears as a small black box.
OBD1 Distributor Sensor: OBD1 distributors lack this sensor under the rotor.
Image: An OBD1 distributor with the cap removed, clearly showing the absence of a sensor directly under the rotor.
5. Distributor Rotation and Click Test
A more hands-on method to differentiate is by manually spinning the distributor’s internal piece that connects to the camshaft.
OBD1 Distributor Rotation: It will click with every slight rotation.
OBD2 Distributor Rotation: It will click only after rotating it halfway. Additionally, OBD2 distributors are generally lighter than OBD1 distributors.
6. MAP Sensor Location
The location of the Manifold Absolute Pressure (MAP) sensor differs between OBD1 and OBD2 Hondas.
OBD1 MAP Sensor (92-95 Hondas): Typically located on the firewall.
OBD2 MAP Sensor (96+ Hondas): Located on the throttle body.
Image: An OBD2 Honda MAP sensor positioned on the throttle body, a key identifier for OBD2 systems.
Why OBD1 Conversion is Popular
Many Honda enthusiasts opt for OBD1 conversions, particularly for older OBD2 vehicles. The primary reasons are:
- Simplicity: OBD1 systems are simpler and monitor fewer parameters compared to the more comprehensive OBD2 systems. OBD2 monitors numerous sensors, and even minor discrepancies can negatively impact engine performance.
- Tuning Capabilities: OBD1 ECUs are significantly easier to tune. The OBD1 ECU code has been extensively analyzed and cracked, allowing for readily available tuning software and modifications. This is crucial for performance enthusiasts who want to customize their engine management system. Popular OBD1 ECUs for tuning include P05, P06, P08, P28, and P72. OBD2 ECU tuning is considerably more complex and was not widely accessible at the time of OBD1’s popularity surge.
Conclusion
Identifying whether your Honda is equipped with OBD1 or OBD2 is straightforward by checking the model year and using the visual cues detailed above, such as distributor plugs, sensor locations, and bolt hole patterns. Understanding these differences is essential for anyone working on Honda vehicles, especially for diagnostics, performance modifications, and engine tuning. For those seeking simpler systems and easier tuning capabilities, particularly for older Hondas, OBD1 remains a popular and viable option.
