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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1073 (Engine Controls Diagnosis - 6.6L (LLY) (DTC P0238 To DTC P0652)) >> Diagnosis >> DTC P0401 >> Circuit Description

Circuit Description

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

The engine control module (ECM) tests the exhaust gas recirculation (EGR) flow once per ignition cycle. When the proper enabling conditions are met, the ECM will close the EGR valve and then open the EGR valve while monitoring the mass air flow (MAF) signal. An expected MAF difference should be detected between the open and closed positions. If the ECM does not see the expected MAF difference, DTC P0401 sets.

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