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Home >> GMC >> 2003 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> Electrical >> Charging Systems >> Charging System >> Diagnostic Tests >> DTC P1638: Pulse Width Modulation Signal Out Of Range >> Conditions For Setting DTC

Conditions For Setting DTC

During the ignition ON test, the PCM detects a PWM signal is out of range.
During the RUN test, the PCM detects a PWM signal less then 5 percent for more than 6 seconds.

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