OBD 2 To OBD1 Conversion Harness

 

This page copied with permission from Trever Cobb,  his site can be found here:   http://t24ever.com/

 

 

K... Here is the promised 99-00 OBD2 to OBD1 (P28) conversion info I promised. Umm... My harness is made to convert an OBD2 (99-00) engine harness (Civic EX, Si, Integra Type R) into an OBD1 harness for use with a P28 (92-95 SOHC VTEC) ECU that has been chipped. These ECUs do not have support for a knock sensor, secondary o2 sensor, crank fluctuation sensor and some other evaporative stuff that didn't exist from 92-95. If you use an OBD1 ECU that needs to have a wire for the knock sensor you will need to figure out where the wire goes on the OBD1 end of the harness. From the OBD2 end it comes from (C3) right next the white/yellow wire going into (C2) and the orange/black wire going into (C1). Edit by Solblu Knock sensor wire added to the table.

I built my converter harness by taking my stock 99 CX ECU and using a grinder to detach the plastic plug/pin part (what else do you call it?) from the circuit board. There are three screws holding it to the board. All three have solder on top of them that if you grind off first you will see the phillips screw head underneath and be able to unscrew it with a small screw driver. We also used the grinder on the underside of the circuit board to basically de-solder the pins from the circuit board.

I bought some 95 Del Sol ECU Plugs (SOHC VTEC) from a local junkyard. I cut the harness about a foot up from the plugs so I had plenty of length on the wires coming out of the plugs.

I then did my research (see my chart below) and got started soldering. It was kind of a bitch to do because the pins are so close together. I realized I needed a way to cover the exposed metal on the wires and pins as well as the solder I was globing on, so I went to a local hardware store and bought several packages of the smallest heat shrink tubing I could find. Then I cut the little tubes to the length I needed, slid them down the wires and after I soldered each one I slid the tube up to cover the exposed metal then used a hairdryer to heat the tubing and make it shrink. It ended up pretty clean looking and I don't have to worry about anything shorting out.


On the OBD1 plugs the wiring scheme is like this (according to the Honda service manual):



On the OBD2 plugs the wiring scheme is like this (according to the Honda service manual):




Here's the crossover list with corresponding OBD1 plug colors:

Function

99-00 Civic ECU

92-95 Civic ECU

92-95 ECU
Plug Wire Colors

 

A1

 

 

 

A2

 

 

 

A3

 

 

 

A4

 

 

 

A5

 

 

PCS

A6

A20

Red

 

A7

 

 

 

A8

 

 

 

A9

 

 

SCS

A10

D4

Brown

 

A11

 

 

 

A12

 

 

 

A13

 

 

 

A14

 

 

 

A15

 

 

FLR

A16

A7

Green/Yellow

ACC

A17

A15

Black/Red

MIL (CEL)

A18

A13

Green/Orange

TACH

A19

A21

Red/Green **

FANC

A20

A12

Yellow/Green

K-LINE

A21

D7

Light Blue

 

A22

 

 

 

A23

 

 

STS

A24

B9

Blue/White

 

A25

 

 

PSPSW

A26

B8

Brown/Red

ACS

A27

B5

Blue/Red

 

A28

 

 

 

A29

 

 

EL

A30

D10

Green/Red

 

A31

 

 

BKSW

A32

D2

Green/White

IGP1

B1

B1

Yellow/Black

PG1

B2

A24

Black

INJ2

B3

A3

Red

INJ3

B4

A5

Light Blue

INJ4

B5

A2

Yellow

 

B6

 

 

 

B7

 

 

 

B8

 

 

IGP2

B9

A25