Ok, this article deals with creating an automatic OBD2a>OBD1 conversion harness and the parts necessary to run an auto OBD2a Accord on an auto OBD1 ecu. You ODB1 guys can also use this info to switch out your Accord ecu for a more ‘freeware friendly’ Integra ecu. Unless you specifically use the parts I did, you may not be successful. All parts discussed here will be USDM parts. I used a P75 auto ecu, a tcu from I believe a 1995 vtec Accord (F22B1) and my engine harness was an OBD2a harness. My car is a 1996 Accord LX sedan.

Ok, this article deals with creating an automatic OBD2a>OBD1 conversion harness and the parts necessary to run an auto OBD2a Accord on an auto OBD1 ecu. You ODB1 guys can also use this info to switch out your Accord ecu for a more ‘freeware friendly’ Integra ecu. Unless you specifically use the parts I did, you may not be successful. All parts discussed here will be USDM parts. I used a P75 auto ecu, a tcu from a '94-'95 non-vtec Accord (F22B2) and my engine harness was an OBD2a harness. My car is a 1996 Accord LX sedan.

1357…… 2468……

12345 678910

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Information provided by Bird333

First off my disclaimer (gotta have one right ). I, nor anyone else is responsible (except you) if you screw up your car, house, life or anything else using this information. USE THIS AT YOUR OWN RISK. Now that’s out of the way, let’s proceed.

I (like maybe some of you out there) wanted to turbo my Accord (still haven’t turboed it yet. One day, one day). As I began to research the idea, I discovered this thing called ‘engine management’. There are various ways to do this, but what seemed to be the safest and relatively cheap was ‘chipping’ a Honda ecu. Well of course I discovered that there was practically no freeware development for an Accord, it was all about Civics and Integras. Also, I discovered that it was all about MANUAL trannies and OBD1 cars. Luck would have it that I would have an automatic tranny and an OBD2 car. So, I thought ‘well I’ll just get an OBD2>OBD1 conversion harness and all will be well’, but soon found out that these harnesses were designed for manual cars and I couldn’t find automatic pinout info for any of these cars. I also found out that OBD1 Accords had a separate tranny computer which further complicated matters. So I was forced to create my own custom OBD2>OBD1 conversion harness that would work with a tranny computer (TCU). So I bought an automatic P06 (Civic) ecu and converted it to a P28 since this seemed to be a popular freeware platform. As I continued to research, I discovered that Civics didn’t use a separate tcu so this purchase was a mistake. I thought all was lost. I needed an OBD1 ecu that had freeware development that also controlled a separate tcu. Thankfully, I discovered that Integras used such an ecu. This article is the culmination of about 2 years (off and on Thanks to the family. ) of research and fabrication.

Ok, this article deals with creating an automatic OBD2a>OBD1 conversion harness and the parts necessary to run an auto OBD2a Accord on an auto OBD1 ecu. You ODB1 guys can also use this info to switch out your Accord ecu for a more ‘freeware friendly’ Integra ecu. Unless you specifically use the parts I did, you may not be successful. All parts discussed here will be USDM parts. I used a P75 auto ecu, a tcu from I believe a 1995 vtec Accord (F22B1) and my engine harness was an OBD2a harness. My car is a 1996 Accord LX sedan.

Parts needed:

1. An Automatic OBD2a>OBD1 conversion harness
2. An AUTOMATIC P75 (94-95 Integra) ecu. (The code on the ecu should look like ****-P75-x5. The ‘5’ in the last section of the code lets you know it is an automatic ecu. The ‘x’ should be an ‘A’ (US 49 state) or ‘L’ (California))
3. A tcu for your engine block. (In my case a F22B2)
4. A ROM from an AUTOMATIC Integra ecu. (I used the USDM OBD1 ‘332’ rom from http://www.pgmfi.org/twiki/bin/view/Library/EcuDefinitionCodes)
5. ECU fuel and ignition maps for your engine that will work in the above rom/bin.
6. Some type of bin editor like Uberdata or Crome.
7. Service manuals for the ecu, tcu and OBD2 engine harness you have. In my case, I needed a ‘94-‘95 Integra manual, a ’94-’95 Accord manual, and a ’96 Accord manual.
8. The necessary parts and equipment to chip your ecu.
9. A chip burner.

NOTES: You may be able to use a manual P75 bin as they may actually be the same code and only behave differently based on the hardware configuration of the circuitboard. If someone wants to test this, please do. You could buy an auto OBD2>OBD1 conversion harness from a dealer, BUT you will need to check to be sure that all the wires match up to the equipment you will be using. Automatic OBD1 ecus and tcus from different cars have slightly different pinouts.

Ok, for people who want to create their own custom harness, here is a parts list:

1. Somewhere in the neighborhood of 100-120 feet of 20 gauge wire.
2. About 10-20’ feet of 18 gauge wire. (Maybe 16 gauge)
3. Wire strippers
4. Crimpers (I got part WM9999-ND at Digikey)
5. 65 contact receptacles (small pins) Tyco part # 175061-1 (-2 is gold if you want them)
6. 26 contact receptacles (big pins) Tyco part # 173631-1 (-2 gold)
7. 2 x 26-pin OBD1 plugs (Tyco part # 174516-6)
8. 2 x 22-pin OBD1 plugs (Tyco part # 174515-6)
9. 1 x 16-pin OBD1 plug (Tyco part # 174514-6)
10. 1 x 104-pin OBD2a pin connector (Tyco part # 179686-6)
11. Soldering equipment (i.e. soldering iron and solder)
12. Digital multimeter.
13. Optional, heat shrink tubing

You can call Tyco and ask for samples of the above parts if you can’t get them from junk ecus and harnesses. They will limit the quantity you can have. DO NOT ABUSE THIS. Get only what you need. Also, try to get a few extra pins just in case you mess up. Here is the conversion table for creating your harness. NOTE: For OBD1 tcu A9 I connected this to the 'Tachometer test wire under the hood. You maybe able to get this signal from OBD2 A20 but I couldn't verify it. If someone could confirm that would make the install even cleaner.

The OBD2a connector will be at right angles so you will have to bend/cut them straight. Now what I did was measure and cut all my wires first and crimped the pins on them before anything else. There will be two parts on each pin to crimp. On the outer end, the crimp should dig into the insulation of the wire. In the middle of the pin, that crimp should go around bare wire. The bare wire should NOT go up inside the socket of the pin. So strip your wires accordingly. If you arrange your ecu and tcu like I did (see pics here about halfway down the page); you will need approx. these wire lengths:

47 pieces of 4-5” wire (you could shorter if you wanted, but it would probably make it hard to work with) these are the wires that will go from the OBD2a connector to the OBD1 ecu plugs.

27 pieces of 21” wire (these go from the ODB2a connector to the OBD1 tcu plugs.)

5 pieces of 19” wire (These go from the OBD1 ecu plugs to the OBD1 tcu plugs. They will have pins at both ends.)

Take note of which OBD1 pin number the pins will go in. The larger openings will use the larger wire and bigger pins. IMPORTANT: This is how you count OBD1 pins. Looking from the side that the wires go in (wire side) with the clip at the top; pin 1 will be the first pin from the left on the top row. Pin 2 will be below it (i.e. first pin from the left on the bottom row.

For example: 1357…… 2468……

IMPORTANT: Counting OBD2 pins is different. Looking from the pin (side opposite the soldering leads) with the clip receptacle at the top, you count across and then go down to the next row.

For example: 12345 678910

On the OBD1 ‘A’ plug pins 1,2,3,4,5,6 and 23,24,25,26 are the bigger holes. On the OBD1 ‘D’ plug pins 1,2 and 19,20,21,22 are the bigger holes. OBD1 ‘B’ plug all holes are small.

A good method I found for soldering my wires to the OBD2 connector was to wrap the wire around a large paper clip in a spiral and then slide the wire over the lead. This helps hold the wire on the lead since most of us don’t have 3 hands. Then just solder the wire to the lead making sure solder gets all around the wire/lead. Try not to heat the lead up too long (no more than 3-4 seconds) or you could melt the plastic that it’s held in. If the lead does get loose try to even it up inside the connector with a similar pin and use a little superglue around the base of it. Be sure you don’t cover the pin with superglue or it won’t have continuity. If you do cover it, just scrap the pin with a sharp knife or something to get the dried glue off.

Once you got all the wires soldered to the OBD2 connector. You will probably want to slide some heat shrink tubing over them down to the base to prevent any shorts. Once I had them all in place, I used a hair dryer to heat them up so they would shrink to the wires. Now it is time to insert the wires into the OBD1 plugs. The wires go in the plugs with the ‘crimp’ side facing up toward the clip. Be careful putting them in the correct locations. They are practically impossible to get back out. You should hear/feel a slight ‘click’ when you have gotten it in all the way. NOTE: You might have to ‘reshape’ the outer crimp a little if you squeezed too flat so it can get in the plug holes. However, be sure the outer crimp is still gripping the wire’s insulation after you reshape it.

Once you got your conversion harness together, it is a good idea to check each pin for continuity with your multimeter.

Now all you need to do is ‘chip’ your ecu. I won’t explain how to do that here. There is plenty of info on how to do that. Finally, take the Integra bin and copy the fuel and ignition maps for your engine into it. Be sure to disable vtec if you don’t have it. Then burn your bin on a chip and install in your ecu. If you did everything right; your car should start with no CELs.

I would like to thank AD, tallh22a, Superorb, Andrew and everyone at Pgmfi.org.

Attached is the conversion spreadsheet sorted by OBD2, OBD1 ecu and OBD1 tcu, and the Integra bin I used.

-Wikied by drdisco69.27.Aug.2005-

• AutoOBDconvertinfoandIntegrabin.zip: Accord Auto Files

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