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Home >> Chevrolet >> 2005 >> Chevy Express H1500, Van Cargo >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 12 (Engine Control System - 6.0L (CNG) - Introduction) >> Description and Operation >> Fuel Injector Control Module Description >> Communication Circuits >> FICM Diagnostic Circuit

FICM Diagnostic Circuit

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The PCM monitors the FICM diagnostic circuit in order to set FICM related DTCs. The FICM diagnostic circuit is a 5 volt circuit that is pulse width modulated by the FICM in order to communicate diagnostic information to the PCM. The FICM Diagnostic Data table indicates the various PWM signals created.

FICM Diagnostic Data

Diagnostic Data PWM Duty Cycle
gasoline operation 25 %
CNG operation 50 %
no input activity for more than 5 seconds 56.25 %
FRT high voltage 62.5 %
FRT low voltage 68.75 %
FRP high voltage 75 %
FRP low voltage 81.25 %
CNG injector fault 87.5 %
FICM internal fault 93.75 %