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Home >> GMC >> 1989 >> Forward Control 3.9 L, Standard >> Repair and Diagnosis >> Engine Performance >> System >> CCC TBI Tests W/Codes >> Testing & Diagnosis >> Diagnostic Materials >> System Check
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System Check

  1. If complaint is "SERVICE ENGINE SOON" light related, this check will lead to the most likely problem area (if a malfunction exists). Enter diagnostic mode by grounding terminal "B" of ALDL connector and record stored trouble codes.
  2. Begin diagnosis with the lowest numbered code shown and go to the numbered trouble code chart. If code "51" is displayed, see PROM or MEM-CAL removal and installation in this article.
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