OBD2 Pinout Diagram: Your DIY Guide to OBD2a to OBD1 ECU Conversion

For DIY enthusiasts and budget-conscious car tuners, understanding the Obd2 Pinout Diagram is crucial when undertaking ECU conversions. This guide provides a clear OBD2 pinout diagram specifically designed for those performing an OBD2a to OBD1 conversion, particularly when utilizing a P28 Uberdata ECU or similar OBD1 ECUs like P30 and P72.

Below is the wiring diagram detailing the connections required for an OBD2a to OBD1 conversion harness. The OBD1 pinouts are listed on the left, and the corresponding OBD2 pinouts are on the right. This diagram simplifies the process, making it accessible for those who prefer to handle their modifications in their garage.

OBD1 Pinout OBD2 Pinout
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 D16
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 OBD2 pinout diagram is also compatible with P30 and P72 ECUs, as well as other OBD1 ECUs, offering versatility for various Honda and Acura models.

For those sourcing parts, remember that OBD2 plugs from automatic transmissions are excellent for this conversion. They often come with extra pins, which can be invaluable when replacing shorter pins during your DIY conversion harness build.

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