The check engine light in your 1991 Honda Civic comes on when a problem exists. The computer reads the information from all of the sensors in the vehicle and triggers the check engine light if a reading is out of specification. Unlike cars manufactured after 1992, the 1991 Honda Civic is not equipped with OBD-II. This means the computer must be jumped with a wire or a paperclip to read the codes.
Locate the service harness. It is under the passenger side of the dashboard and is green in color.
Bend the paperclip into a "U" shape.
Plug the paperclip into the left side of the harness pins. One side of the clip plugs into one pin and the other end plugs into the pin next to it.
Turn the vehicle to the "ON" position, but do not start it.
Observe the check engine light as it blinks. There will be both short and long blinks. Codes 1 to 9 are all short blinks and 10 to 43 are a combination of short and long. The number of long blinks equals the first digit while the number of short blinks equals the second.
Compare the code to the reference provided for the description of the code.
