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Re: GM charging system, codes P1637 P1638
Posted to Technical Discussion Forum on 2/24/2017 3 Replies

Sam, I didn't have time to review the schematic wiring diagram when I first replied to your post, because I had to do a wheel alignment. The "S" terminal is not used. If the wiring is good from the PCM to "L," then run a 500 ohm, 1/2 watt resistor, from switch... Login to read more.

3 Replies Received (View Replies)