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Home >> Chevrolet >> 1997 >> C3500 HD 7.4 J, Automatic >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 3 (Engine Controls - Tests W/Codes - 6.5L) >> Diagnostic Trouble Codes >> DTC P1643 - Wait To Start Light Control Circuit >> Circuit Description

Circuit Description

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The WAIT TO START light is illuminated by the PCM when the glow plugs are commanded on. When the PCM is commanding the WAIT TO START light on, the voltage potential of the circuit will be low (near zero volts). The the PCM is commanding the WAIT TO START light off, the voltage potential of the circuit will be high (near battery voltage).

The primary function of the PCM is supply ground to the WAIT TO START light circuit.

DTC will set when the following conditions are present:

Or