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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1040 (Engine Controls Diagnosis - 4.3L (DTCS P0140-P2610)) >> Diagnosis >> DTC P0442 >> System Description

System Description

WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

This diagnostic tests the evaporative emission (EVAP) system for a small leak when the ignition is turned OFF, and the correct conditions are met.

Heat from the exhaust system is transferred into a vehicle fuel tank while the vehicle is operating. When the ignition is turned OFF, a change in the fuel tank vapor temperature occurs. With the EVAP system sealed, this results in corresponding pressure changes in the fuel tank vapor space. This change is monitored by the control module using the fuel tank pressure sensor input. The control module then makes a judgement on the integrity of the system. With a 0.51 mm (0.020 inches) leak in the system, the amount of pressure change observed is significantly less than that of a sealed system.

If the control module detects a pressure change less than a calibrated amount, DTC P0442 sets.

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