OBD-I What should you know-How do you read it.

How OBD-I is connected to the console of a car.

OBD-I was used during the earlier years of the car manufacturing industry.

So, How Do You Test It (Without A Code Reader Or Scan Tool)


Once in diagnostic mode, the computer flashes the Check Engine or Service Engine Soon light (the specific name varies by year) in a fashion similar to Morse code. Each code is a series of flashes followed by a pause, and then a second series of quick flashes. (Note: When this diagnostic mode is evoked, the first code is always 12—one flash and then two quick flashes. This code signifies no distributor reference signal, and, since the vehicle is not running at this time, this is correct.

The Paper Clip Test
To find the trouble codes being set, jump the A and B pins of the 12 pin OBD-I connector with a paper clip. While the car is off, sitting still, turn the ignition key forward while this jumper is in place.

Do not start the car. The Service Engine Soon ( SES ) light will flash in a repeating sequence, telling which trouble codes have been set in the ECM. This paper clip method will tell you the trouble code or codes set in your ECM, but it will not tell you what conditions the trouble code is being set under, or let you clear the trouble codes on the fly, as the ALDL cable and PC setup will.

Choose Your Help Topic Below

 ’81-’95 diagnostic trouble codes
Note: Not all codes apply to all years and models Also with OBD1 each car maker used their own codes and definitions for identifying failures in the computerized engine management system. As a result, This made it difficult for auto mechanics servicing multiple vehicle brands.