How To Convert OBD2 to OBD1

How To Convert OBD2 to OBD1

By
John Huh
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Converting your OBD2 ignition distributor to OBD1 operation for the purpose of your Honda engine swap is often the only way to really reach your goals. The benefits of a chipped OBDI ECU far outweigh the issues you may have to wade through to see your Honda swap project to the end.

But it can also be daunting considering the amount of distributors out there and the many different possibilities. That’s why we’ll be taking a look at exactly how to convert OBD2 to OBD1 in this walkthrough guide. Going from one generation of OBD to another is not always the easiest, but can be done quickly and easily using our How to Convert OBD2 to OBD1 article.

Let’s begin by taking a look at the distributors to choose from when performing this conversion.

Honda OBD1 Distributor

 

Let’s start with the OBD1 Distributor, or the target of this how-to guide. Below is the OBD1 distributor that you’ll be converting to, so take this time to familiarize yourself with the distributor plug pinout.

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This OBD1 distributor can be found in the 1992-1995 Honda Civic, the 1992-1995 Acura Integra and is comprised of two plugs, with nine pins total.

The part number for this distributor is 30100-P08-006 from Honda, but can also carry the part numbers 30100-P08-006 or TD42U. Next up we’ll be looking at the OBD2 distributor and wiring diagram in our How To Convert OBD2 to OBD1 walkthrough guide.

HONDA OBD2 DISTRIBUTOR

 

The OBDII Honda D and B series distributors are slightly different in the wiring diagram, but our article makes this conversion a breeze.

how-to-convert-OBD2-to-OBD1-8

This OBD2 distributor is found in all 1996-1998 Honda Civics, as well as the 99-2000 OBD2B B16 Civic SI, as well as all Integras from 1996-2001.

This distributor is also known as the “Big Plug” as it combines the two plugs found on the OBD1 unit together.

how-to-convert-OBD2-to-OBD1-9

 

The Big Plug ignition distributor wiring diagram is as follows.

  • ICM Ignitor – Yellow / Green
  • CKP Crank Position + reference – Light Blue
  • CKP Crank Position – reference – White
  • CYP Cylinder Position + reference – Yellow
  • CYP Cylinder Position – reference – Black
  • TDC Top Dead Center + reference – Green
  • TDC Top Dead Center – reference – Red
  • RPM Lead Signal – Dark Blue

The part number for this OBD2 distributor is 30100-P73-A02 from Acura or Honda, but can also carry the part numbers 30105-P73-004 or 30100-P73-A02.

There’s one more exception to the OBD2 distributor in the OBD2b distributor found in late model Hondas. In contrast to the “Big Plug” found on the normal OBD2 distributor connector, the OBD2b distributor is known as the “Small Plug”

Found in the 1999-2000 Honda Civic SOHC ( NON SI ) models this single 7 pin plug varies slightly from it’s OBD2 brother.

The small Plug ignition distributor wiring diagram is as follows.

  • ICM Ignitor – Yellow / Green
  • CKP Crank Position + reference – Blue
  • CKP Crank Position – reference – White
  • CYP Cylinder Position + reference – Yellow
  • CYP Cylinder Position – reference – Black
  • TDC Top Dead Center + reference – Green
  • TDC Top Dead Center – reference – Red

The OBD2B plug does not require a RPM signal because your P2P or P28 ECU controls it. If you are swapping from OBDIIb to OBDI you will need to add this wire to your conversion wiring harness.

You now know How To Convert OBD2 to OBD1 in your Honda, please let us know if you have any questions below!

Need more Honda swap information? Check our guides below!

 

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12 COMMENTS

      • Hi Daniel, thanks for commenting.

        Yes it is possible to go from OBDI to OBDII and vice versa! of course one is easier than the other, but if you are stuck with one type of dizzy and need spark it’s very easy to do!

    • Hi Cory! thanks for commenting.

      Which wire in the OBD2 to OBD1 conversion did you have a question about sir? Let me know and I can help! Thanks for commenting!

    • Hey Will, thanks for reading

      yes you can convert OBD2A to OBD2B, but unless you are picking up a cheap Honda conversion harness there’s not much money to be saved over buying a 2B ECU from the jump. Hope that helps

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