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<\/a><\/p>\nFig. 1<\/strong><\/p>\n <\/p>\n Door Latch Actuators is the third topic in the TechLink series highlighting several of the related systems handled by the Body Control Module (BCM) on GM models built with the Vehicle Intelligence Platform (VIP). The goal of this series is to help improve understanding of the components operated by the BCM and reduce warranty claims and unnecessary component replacement.<\/p>\n The earlier systems in the series are the Keyless Entry System<\/strong><\/a> and Content Theft Deterrent<\/strong><\/a>.<\/p>\n COMPONENT BREAKDOWN<\/strong><\/p>\n LATCH SEQUENCE<\/strong><\/p>\n Once the BCM receives a lock\/unlock request from a door lock switch, Remote Keyless Entry transmitter (key fob), passive-entry system, or another vehicle function, it checks conditions such as vehicle state, door status, child security logic and command arbitration. (Fig. 2) It then energizes the appropriate half H-bridge polarities for a short period, and the latch motor moves the lock or release mechanism.<\/p>\n Fig. 2<\/strong><\/p>\n <\/p>\n BASIC OPERATION<\/strong><\/p>\n Proper operation of the door latch system requires smooth mechanical operation of all associated components. When diagnosing a concern with a door latch system, always perform a thorough visual inspection of the door latch and any associated cables\/linkages. Look for any mechanical issues that may prevent proper operation of the latch prior to performing extensive electrical diagnosis.<\/p>\n The BCM determines and controls the door lock state through various inputs from the keyless entry system, theft deterrent system, interior door lock switches and door handle switches. Depending on the style of door latch, door lock state and the input commanded, the BCM energizes the appropriate half H-bridge polarities for a short period to command the appropriate lock or release actuator to perform the desired operation.<\/p>\n Latch Motors<\/strong><\/p>\n The latch motors are driven through two control legs:<\/p>\n The BCM controls the door actuator control circuit output voltage and polarity using multiple half H-bridge circuits similar to the diagram shown below. (Fig. 3)<\/p>\n Fig. 3<\/strong><\/p>\n <\/p>\n The BCM supplies motor voltage and ground in the appropriate polarity for approximately 200 ms via the half H-bridge control circuits to execute functions such as power lock, power unlock, release, double-lock, and undouble-lock.<\/p>\n The BCM\u2019s output-driver diagnostics monitor the commanded output electrically \u2014 primarily output voltage and current behavior \u2014 not just whether the latch mechanically moved. The half H-bridge hardware reports open circuit, short-to-ground, short-to-battery and controller-specific faults. Detected faults will trigger DTCs, which can disable the output.<\/p>\n DOOR LATCH STYLES<\/strong><\/p>\n There are two main styles of door latches used across GM vehicles with the VIP electrical architecture: conventional-style latches and E-Latch assemblies.<\/p>\n Conventional latches are found on most Chevrolet and GMC vehicles, while E-Latches are found on most Cadillac vehicles and Corvette models. (Fig. 4)<\/p>\n Fig. 4<\/strong><\/p>\n <\/p>\n Conventional Latches<\/strong><\/p>\n Conventional door latches have two mechanical cables attached to an exterior and interior door handle. The operation of these door latches is simple: when the BCM commanded door lock state is LOCK, the BCM commands the door latches to the locked state. When a conventional latch is in the locked state, a pull on the exterior handle will not release the latch. Two pulls of the interior handle while the latch is in the locked state will release the latch, i.e., the first pull unlocks the latch and the second releases the latch. (Fig. 5)<\/p>\n\n
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