My '87 GMC is throwing a code

Discussion in 'General Chevy & GM Tech Questions' started by MD4x4 Fireman, Dec 18, 2008.

  1. MD4x4 Fireman

    MD4x4 Fireman Epic Member 5+ Years 1000 Posts

    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?
  2. Badbrad469

    Badbrad469 Rockstar 100 Posts

    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. MD4x4 Fireman

    MD4x4 Fireman Epic Member 5+ Years 1000 Posts

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

    GaryL Epic Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    You want to jump between A and B

  5. retired

    retired Rockstar 100 Posts

    Badbrad got it right.
  6. MD4x4 Fireman

    MD4x4 Fireman Epic Member 5+ Years 1000 Posts

    can i do it while going down the road?
  7. Badbrad469

    Badbrad469 Rockstar 100 Posts

    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. JMoney02

    JMoney02 Epic Member 5+ Years 500 Posts

    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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