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  1. #1

    Question My '87 GMC is throwing a code

    My 1987 GMC Sierra is throwing a code randomly when I am driving. I was told I can use a paper clip in the computer port under the dash to view it by counting the flashes since I cant find a cheap code reader. Which ports is it? Has anyone done this? Where can I look up the codes?
    1987 GMC Sierra Classic 5.7TBI

  2. #2


    on my 91 gmc i do this when the cel comes on. just take a paperclip and "jump" the last two holes on the top row. turn the key on, but don't start. it will flash once then twice to show it's entering the read out mode(it will flash this code 3 times) then it will flash the actual code that's being thrown. say code 23 will be "flash flash; pause; flash flash flash" this will also happen 3 times. lastly it will flash 12 again to show it's finished. if u have a chiltons or haynes manual, it will have the obd1 codes in it. hope this helps out a little

  3. #3


    Ill give it a shot. I was also told that its the first and 4th on the top row?

  4. #4


    You want to jump between A and B


    99 K 1500 Suburban
    78 Silverado Big 10 w/factory 454
    00 S-10 Blazer
    1976 Trans Am
    1980 Honda CB900 Custom

  5. #5


    Badbrad got it right.

  6. #6


    can i do it while going down the road?

  7. #7


    Quote Originally Posted by MD4x4 Fireman View Post
    can i do it while going down the road?
    no, u do the same as if u plugged a scanner up to it. jump the pins, turn the key over(not starting it) and count the flashes. like i said, my blazer flashed "12" three times, then the code three times, then "12" again.

  8. #8
    Master Mechanic
    Join Date
    Oct 2008
    Brandon, FLA
    Blog Entries


    Definitely NO while driving the vehicle, the OBD1 system was not meant for driving in the OPEN LOOP
    mode. It was to energize the system and get the code back from the PCM and feed it through the CEL, the system was just the beginning of end since regulator's want the systems for all vehicles the same(OBDII). Paper clip is ok, I pefer a short jumper wire with clips on either end. Do not ground them together though, you will cause issue's with the PCM.

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