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Home >> GMC >> 1998 >> Forward Control 6.5 Y, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 6.5L Turbo Diesel >> Self-Diagnostic System >> Diagnostic Procedure >> Diagnostic Procedure

Diagnostic Procedure

  1. Ensure all non-electronically controlled systems are operating properly. DO NOT proceed with testing unless all non-electronically controlled system problems are repaired.
  2. ALWAYS begin diagnosis with On-Board Diagnostic (OBD) system check to determine if transmission and PCM are working properly. If DTCs are displayed, determine if they are hard or intermittent trouble codes.
  3. A hard code is present when 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 TURBO DIESEL article.
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