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Home >> GMC >> 1996 >> Forward Control 7.4 J >> Repair and Diagnosis >> Engine Performance >> Theory and Operation >> Engine Controls - Theory & Operation - Diesel >> Fuel System >> Fuel Control >> Glow Plugs
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Glow Plugs

Glow plugs are small 6-volt heaters, powered by 12 volts to give rapid heating. PCM operates glow plugs, which cycle on when ignition switch is turned to the RUN position (prior to starting the engine). The glow plugs remain pulsing a short time after engine starting, then automatically turn off. For diagnostic information on computer controlled system, see appropriate TESTS W/CODES article.

CAUTION: Using a jumper wire on by-pass relay will cause glow plug to fail.