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International Automotive Technicians Network
Re: 2002 astro van 4.3 x code p1637 Whats the deal?
Posted to Technical Discussion Forum on 3/14/2007

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The PCM sends 10 volts over the L circuit to turn on the alternator. It does not send a PWM signal nor does it control field voltage. The PCM only turns on the alternator and the internal regulator co... Login to read more.