Converting from OBD2 to OBD1 for your ECU might seem daunting, but with the right wiring diagram, it becomes a manageable DIY project. This guide provides a straightforward Obd2 To Obd1 Wiring Diagram, perfect for those working on a budget and who enjoy hands-on car modifications. Whether you’re upgrading to a P28, P30, P72, or another OBD1 ECU, this diagram will serve as your roadmap.
Understanding the OBD2 to OBD1 Conversion
Before diving into the wiring, it’s crucial to understand why this conversion is sometimes necessary. Older OBD1 ECUs, like the popular P28, P30, and P72, are often favored in performance tuning for their simplicity and readily available aftermarket support. When installing these ECUs in vehicles originally equipped with OBD2 systems, a conversion harness or manual wiring is required to bridge the gap between the different pinouts. This diagram specifically outlines the pin-to-pin connections needed for a successful OBD2 to OBD1 ECU swap.
OBD2 to OBD1 Wiring Diagram Pinout
Below is the wiring diagram that details the connections between OBD2 and OBD1 ECU plugs. The OBD1 pinouts are listed on the left, and the corresponding OBD2 pinouts are on the right. Follow this chart carefully to ensure correct wiring for your conversion.
| **OBD1 Connector (Left) | OBD2 Connector (Right)** |
|---|---|
| A1 | A4 |
| A2 | A1 |
| A3 | A3 |
| A4 | A8 |
| A5 | A2 |
| A6 | A6 |
| A7 | A16 |
| A8 | No Use |
| A9 | A12 |
| A10 | No Use |
| A11 | No Use |
| A12 | A27 |
| A13 | A18 |
| A14 | No Use |
| A15 | A17 |
| A16 | A19 |
| A17 | A26 |
| A18 | No Use |
| A19 | No Use |
| A20 | A15 |
| A21 | A20 |
| A22 | No Use |
| A23 | A10 |
| A24 | A23 |
| A25 | A11 |
| A26 | A9 |
| ————————- | ————————– |
| B1 | A24 |
| B2 | A22 |
| B3 | No Use |
| B4 | Blank |
| B5 | C5 |
| B6 | Blank |
| B7 | C29 |
| B8 | C16 |
| B9 | C6 |
| B10 | C18 |
| B11 | C4 |
| B12 | C14 |
| B13 | C3 |
| B14 | C13 |
| B15 | C2 |
| B16 | C12 |
| ————————- | ————————– |
| D1 | C10 |
| D2 | D5 |
| D3 | D6 |
| D4 | C7 |
| D5 | No Use |
| D6 | C15 |
| D7 | C8 |
| D8 | No Use |
| D9 | C17 |
| D10 | C16 |
| D11 | D1 |
| D12 | No Use |
| D13 | D2 |
| D14 | D7 |
| D15 | D8 |
| D16 | No Use |
| D17 | D3 |
| D18 | No Use |
| D19 | D4 |
| D20 | D10 |
| D21 | D12 |
| D22 | D11 |
| ————————- | ————————– |
This wiring diagram is compatible with P28, P30, P72, and other OBD1 ECUs, making it versatile for various Honda and Acura applications.
Tips for Using the Wiring Diagram
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Double-Check Pinouts: Before making any connections, always double-check the pin numbers on both your OBD1 and OBD2 connectors against this diagram. Mistakes in wiring can damage your ECU or vehicle.
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Automatic OBD2 Plugs: For those sourcing their own connectors, consider extracting OBD2 plugs from automatic vehicles. These often have extra pins that can be useful replacements if you find any pins are short or damaged during your DIY process.
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Clean Wiring: Ensure your wiring is clean and well-insulated. Avoid exposed wires to prevent shorts and electrical issues.
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Test Thoroughly: After wiring, test all ECU functions to confirm proper connection and operation.
By following this OBD2 to OBD1 wiring diagram and taking your time, you can successfully complete your ECU conversion. This guide aims to provide a helpful and budget-friendly solution for your automotive DIY needs.
