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Home >> Chevrolet >> 2021 >> Trailblazer L >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Vehicle Access System >> Diagnostic Information and Procedures >> DTC P257D-P257F >> Circuit/System Description

Circuit/System Description

For an overview of the component/system, refer to Hood Ajar Indicator Description and Operation 

Circuit Description
Signal Terminal B The control module input circuit has an internal resistance connected to 12 V. Regulated voltage supplied by the control module.
Signal Terminal A The control module input circuit has an internal resistance connected to 12 V. Regulated voltage supplied by the control module.
Ground Chassis Ground
Component Description
B55 Hood Ajar Switch In addition to the switch, the assembly also contains 3 resistors and 2 diodes, all of which are in series. The output of the switch that is connected to the body control module changes its resistance to ground from 732 ohms to 2112 ohms when the hood is opened. The output to the engine control module does the opposite. Because of diodes inside the component, the resistance can not be measured with a standard DMM.
K9 Body Control Module The module controls various vehicle functions like lighting, central door locking, power windows, etc.
K20 Engine Control Module The control module contains a microprocessor used to process input data to control outputs.
The control module controls a series of actuators to ensure optimal engine performance. The control module does this by reading values from a variety of sensors, interprets the data and adjusts the engine actuators accordingly.
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