Converting your OBD0 to OBD1

Converting your OBD0 to OBD1


The following is a guide on how to convert your OBD0 Honda to a OBDI, with relative ease. To complete this converting your OBD0 to OBD1 article and take your performance vehicle to the next step, you will need the following parts :

  1. An obd1 distributor that matches your motor setup
  2. A distributor adapter allowing you to plug your new distributor up
  3. A obd1 ecu that will correctly run your motor setup
  4. An ecu adapter harness allowing you to plug in your new ecu.
  5. A four wire o2 sensor

Need OEM parts? Pro Street OEM Parts

For our example, we will be converting a CRX Si w/B16A & OBD0 ECU to a P28 OBD1 ECU. Many times we get the question, ‘Why bother converting to OBD1?’ Well for most customers planning on an EEPROM flashing solution such as Uberdata, Chrome or Neptune, you will need an OBDI ecu to achieve this.

When you factor into the equation the cost of parts you will be selling once you complete the task, it really seems like a small price to pay for the ultimate ability to tune a vehicle. That makes converting your OBD0 to OBD1 well worth the modification dollars.

You will need to replace your old distributor with an OBD1 version. Make sure you match the engine. For example, if you have a B-series VTEC engine, you’ll want a Del Sol, GSR, or Type R distributor. Others may work that I’m not familiar with, but I wasn’t going to risk it. If you have a D-series, then get one from a Civic. Just make sure it’s OBD1.


Now you will need to convert your existing harness to plug into this new OBDI distributor. You can do this one of two ways, either put OBD0 plugs on your new distributor, or put OBD1 plugs on your engine harness.

We prefer the second option, as that leaves your new distributor stock and resellable should you decide to go that route.

Engine Harness OBD1 Distributor

Peach White
White/Blue White/Blue
Blue/Yellow Blue/Yellow
Thin White Peach
Peach/Blue Peach/Blue
Blue/Green Blue
Fat White Yellow/Green

The wires on the two pin connector had the same colors so I did not bother to list them above. Once the wiring is taken care of, simply bolt up the distributor (make sure the shaft is turned the proper way and isn’t 180 degrees off) and then plug it into the harness.

Oxygen Sensor
One of the differences between the OBD0 B16A and an OBD1 B-Series motors is the fact that you have to convert from two 1-wire oxygen sensors to one 4-wire oxygen sensor with heated wires. In order for the ECU to operate correctly, you will need to place the new sensor downstream from the original locations so that it can read all four cylinders. Normally there is additional wiring involved, because you have to add wires for the senor’s heater.

Conversion Harness
We really recommend the use of a Boomslang harness, as this will eliminate a ton of wiring hassle. When using such a flying loom, install of your new ecu is very straightforward, tidy and simple.



You will notice that there are several wires that are not hooked up. These wires include those for VTEC, Oxygen Sensor, CEL jumper, etc. I will not go into detail here because the instructions that are provided are very thorough and straight forward.

-Knock sensor goes to pinout D3 on the ecu
-Vtec pressure switch goes to pinout D6 on the ecu
-Vtec solenoid goes to pinout A4 on the ecu
-IAB (gsr B18C) goes to pinout A17
-O2 sensor heater control. One of the blacks on the o2 sensor go to pinout A6 at the ecu
-O2 sensor signal. White on the o2 sensor goes to pinout D14 on the ecu
-The other black on the sensor is a switched 12 volt. Splice into pinout A14
-Green or gray on the o2 sensor is the o2 ground. Splice into pinout D22

Enjoy your new OBDI vehicle!


  1. Do you guys know anything about Auto Swaps?? I have an Automatic Tranny from a 91 integra LS. And have a P75 OBD1 Ecu. And I have a B20 Engine. Is there a way to make that tranny work with the OBD1 Ecu?

    • Hi Gime on the cob, thanks for reading and commenting.

      So can you go over your setup again? You’ve got a 91 integra LS that was already auto correct?. And have a P75 OBD1 Ecu, its OBDI?.

      And I have a B20 Engine, is that OBDI or OBDII?. And lastly what is the code on your transmission?

      • The transmission if OBD0…. ANd the P75 ECU is OBD1. And I have a 1993 Civic Automatic.
        I got a 2.0 B20 That came off a 4 wheel drive Prelude. I have the Hole car but that prelude tranny is shot.
        ANd i got an Obd1 Tranny that came off a 91 integra. No kick down cable on that tranny.
        ANd i got a p75 OBd1 ECU in the garage.
        My main question is can i make that tranny work with an OBD1 ECU. ANd yes the tranny is automatic.

      • *****The transmission if OBD0…. ANd the P75 ECU is OBD1. And I have a 1993 Civic Automatic.
        I got a 2.0 B20 That came off a 4 wheel drive Prelude. I have the Hole car but that prelude tranny is shot.
        ANd i got an **Obd0 Tranny that came off a 91 integra. No kick down cable on that tranny.
        ANd i got a p75 OBd1 ECU in the garage.
        My main question is can i make that tranny work with an OBD1 ECU. ANd yes the tranny is automatic.

        I should have proof read it.

        • Gotcha Gime on the cob.. you can make this swap work but you’ll need a lot more to get it to go into your 93 Civic, probably way more than it’s worth.

          We would recommend picking up a OBD1 transmission, and you’ll be set! Let us know if you have any other questions!

          • THanks i was thinking the same thing… but i got this obd0 transmission in the garage just sitting there.. idk what to do with it..

  2. How many more things would i need to buy to make that transmission work?? Just to get an ideah. Remember i don’t pay for labour since my best friend is a mechanic. And a lot of simple parts can be bought at a junk yard.

  3. Hi my name is keston and i have a 1991accord ex.want to put a 2.3ltr vtec in but none of the honda specialist here can do the conversions.i read ur report an realize its possible want ur expert advice an list for them i love my car .

  4. I’m new to swaps and I want to swap in a B16 into my ED6. What would I need to complete this swap and any instructions?

    • Enrique, thanks for reading.

      Your swap definitely sounds like it’s headed in the right direction, the instructions you’ll want to pay attention to in this guide refer to OBDO to OBDI. This is the easiest swap for you, because jumping up to OBDII will require more a crank position sensor.

      Let us know how the swap turns out, and if you need any more pointers.

      Thanks for commenting!

  5. Hello I just recently dropped in what I want to end up being a mini-me swap into my obd0 89 crx si

    What I want to know is this, will my car run in this current set up ?

    D16z6 head , distributor
    JDM D15b block
    Obd0 D16a6 alternator , intake

    P3 3000 si tranny obd0

    I’m buying the obd1 p28 ecu and the obd0 to obd1 conversation kit

    Also how do I hook up the vtec selenoid with the original obd0 wire harness ?

    I greatly appreciate the assistance as this is my first swap of hopefully many to come.

    • Hi Deliano, thanks for reading!

      Yes this setup should run fine, are you sticking with the stock pistons? if you are swapping in higher compression pistons, you’ll need to clay it to make sure it clears and doesn’t hit anywhere of course.

      Hooking up the VTEC solenoid will be easy to do, just run the wires through your harness or run wires directly to your P28 ECU, here’s an article for you to check out :

      Thanks for commenting! Sounds like an awesome SOHC build!

      • So I just finished the mini-mi swap in my 89 crx, went to start and fuel pump didn’t kick in. But Main relay clicked on
        Checked fuses , Alternator Solenoid fuse is blown, #14
        Put a new fuse in
        Unplugged fuel pump , clicked over my ignition and it blew
        Unplugged Main Relay and bypassed to start and fuse blows
        Unplugged alternator, blew fuse
        Unplugged dizzy , blew fuse still

        Does this mean it’s a for sure short within the wiring ? Or could it be another device I’m not seeing on this circuit

        Need this car up and running ASAP, been messing with it for 2 days and no luck any help would be awesome and greatly appreciated as it is my daily driver !

        • Hey Deliano, so quick question, is this the factory harness? have you checked over the harness? Is your alternator showing continuity between the fuse box and the ground?

  6. Alright so, after blowing fuse #14 4 times i found that my fuel pump was totally shot and grounding out . Fault caused the power wires running to my pump to fail, ran a new lines .

    got a new fuel pump In and working

    I no longer blow fuse #14

    Went to start it but for some reason it doesn’t want to ignite.
    Turns over
    Ecu is fine
    Main relay primes and pump kicks in strong.

    Have spark to the ends of my spark plugs and getting fuel to my rail

    Now my CEL gives me 2 solid flashes and one quick flash indicating it error code 21, read it was my vtec, which I haven’t hooked up since I’m missing the plug BUUT it doesn’teffect the way it starts .

    Sprayed starter fluid into the intake to see if it would sustain but died out shortly after firing up.

    I’m thinking maybe it’s out of timing ?
    Crank sensor or camshaft positioning sensor ?
    Or is it cause I’m using obd0 injectors/intake ?

    Mind my build is d15b vtec engine
    P28 ECU
    With a obd0 a6 intake and injectors

    I have exhausted all my brain power and knowledge! So I hope someone posses the answer I need .

    • Phew.. sounds like a long journey but you are close! Code 21 shouldn’t stop your car from starting.

      1. Fuel pressure – how much of it do you have?
      2. fuel injectors – have you confirmed with a noid light that your injectors are firing?
      3. If you have spark and the car starts, but dies after putting in starting fluid, I would guess that your injectors aren’t firing. Test them using a digital multimeter

      I think you are close! just need to figure out this last bit. Here’s a few guides to help you.

      Let us know what happens!

      • Okay I’m going to check this stuff asap, can I buy those noid lights at an auto zone or someplace simular ?
        My dad was guessing fuel pressure

        I was guessing maybe my injectors were firing at the wrong time , if that’s even possible… but I’ll be checking this I’m the morning,

        I recently converted to obd1 injectors and bypassed the resistor box .

        • I would test the injector directly using the Honda Civic fuel injector testing guide first, then work backwards from there.

          1. check injector pulse
          2. test injectors
          3. Measure fuel pressure
          4. check pump

          That should uncover something. I think we did post the article and DIY How To test your Civic injectors, let us know if that worked for you!

  7. Iam going to buy a set of noidstoday, is there a specific type to buy? Like one geared just for Honda injectors?
    Also, pulled my plugs and they were all black.
    We cleaned them when we put them in

    • Hi Deliano! Yes! you can get noid lights made for your Honda at any parts store.. If your plugs are black, were they black AND wet? or just sooty? What part number or heat range of plug are you using?

    • Hrm okay if you have a weak injector signal typically that’s not enough to cause your spark plugs to foul.

      When you say you did a voltage test, which test is it? of the injector plugs? did you measure the resistance of your injectors yet? and what spark plugs are you using in your Honda?

  8. I tested the voltage with a multimeter going to the injectors , each one , I was told each fuel injector must recieve 11.5-12v in order to work.

    I just found out that I was sold obd0 injectors but told they were obd2….. so I went back to the resistor box cause they pulled 2.5 ohms each.

    I checked my ecu and it’s alright still , didn’t fry it.
    Only error code I still get is 21. Vtec

    I just bought some Autolights sparkplugs from autozone and am about to imstall
    cause they didn’t have ngk….

  9. I just removed my main relay and jumped it, started right up. Funny thing I have 3 relays…. I guess all bad…
    Now the issue is my idle is at like 3000, and my throttle is stuck in the open position?
    I’m buying the relay right now, hope that fixes my idle issue.