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Home >> GMC >> 1995 >> Forward Control 4.3 Z, Automatic >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 6.5L Diesel. >> Self-Diagnostic System >> Diagnostic Procedure >> Diagnostic Procedure
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Diagnostic Procedure

  1. Ensure all non-controlled systems NOT related to the Diesel Electronic Control (DEC)/electronically-controlled transmission systems are operating properly. DO NOT  proceed with testing unless all non-DEC/electronically-controlled transmission systems problems are repaired.
  2. ALWAYS begin diagnosis with On-Board Diagnostic (OBD) system check to determine if DEC/electronically-controlled transmission systems and PCM/TCM are working properly. See appropriate ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK chart. If trouble codes, other than Diagnostic Trouble Code (DTC) 12 are displayed, determine if they are hard or intermittent trouble codes.
  3. A hard code is present while working on vehicle, and problem persists. Hard codes will cause Malfunction Indicator Light (MIL) to come on.
    NOTE: SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).
  4. An intermittent code does not reset itself and is NOT present while working on vehicle. Intermittent codes are often caused by loose connections. MIL will go out 10 seconds after fault goes away. For intermittent diagnostic procedures, see TESTS W/O CODES - 6.5L DIESEL article.
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