2002 GMC Yukon Electrical Voltage Drop

2002 GMC YUKON
167,000 MILES
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PUDERIF
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  • 2 POSTS
Replaced the alternator/voltage regulator last year and the battery this year. Voltage drops from approx. 14.5 to 13 intermittently on hot days or when engine at operating temps in stop & go traffic. Connected scanner and issue appears to most frequently occur at 198+ degrees although sometimes lower. Periodically the charge system dummy light comes on due to code P1637, likely the result of the voltage drops straining the charging system and battery.
Any idea what components to check for shorts/failure that activate when coolant temp sending unit is over 198?
Aug 29, 2013 at 12:43 PM
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JACOBANDNICKOLAS
  • CERTIFIED EXPERT
  • 110,175 POSTS
Even at 13 volts, the alternator is producing. Is there a specific time this happens? Have you checked the alternator output when the volts drop? The regulator itself may be the issue here. Have you ever had the alt load tested at a parts store?
Aug 29, 2013 at 7:01 PM
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PUDERIF
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The alternator and voltage regulator test good.

When the coolant temp exceeds 198 degrees on hot days (over 90 degrees) or in stop & go traffic, it appears a circuit is shorting out causing the drastic voltage drop. This occurs even after installing a new battery and alternator/voltage regulator.

Over an extended period, the alternator/voltage regulator burns out and needs to be replaced again.
Sep 6, 2013 at 1:53 PM
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