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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 429 (Engine Controls Self-Diagnostics - 6.0L Bi-Fuel & CNG) >> Diagnostic Tests >> DTC P1204: Vehicle Does Not Start On CNG >> Circuit Description

Circuit Description

WARNING: This page is about a different car, the 2003 GMC Savana and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) controls fuel delivery and for KL6 vehicles, determines which fuel system the engine is operating on. The PCM controls the Low Pressure Lock-Off (LPL) solenoids, and the High Pressure Lock-Off (HPL) solenoids. The PCM commands the HPL solenoids open for one second at every ignition ON, in order to prime the CNG fuel system. The PCM commands the HPLs, and the LPL open, when the engine is cranking or running on CNG. This DTC sets if the vehicle does not start on CNG within 4 seconds.

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