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Home >> GMC >> 1996 >> C3500 HD 6.5 F, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing - Diesel >> Fuel System >> Inhibit Switch (Black Cap)
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Inhibit Switch (Black Cap)

  1. Remove connector from inhibit switch when engine temperature is less than 100°F (38°C). Inhibit switch is located in water crossover near front of engine. Set ohmmeter on low range. Test continuity across switch terminals. Switch should be closed (a reading of less than one ohm on ohmmeter).
  2. Test terminals for continuity to ground with a test light to battery voltage or ohmmeter on high scale. Light should be off. Meter should show greater than one megohm resistance. Replace switch if results are not as specified.
  3. Disconnect plug from switch terminals when engine temperature is greater than 125°F (52°C). Change ohmmeter setting to highest scale or use a self-powered test light. Test continuity across switch terminals. Test continuity from each terminal to ground. Switch should be open (test light off or high ohm reading of greater than one megohm on ohmmeter) and resistance to ground should be infinite. Replace switch if it is closed or if shorted to ground. When installing replacement switch, tighten to 17 ft. lbs. (23 N.m).
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