Common Symptoms of a Faulty Body Control Module (BCM)

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The capabilities of Electronic Control Units (ECUs) in modern vehicles are expanding rapidly, not only in terms of quantity but also in complexity. One of the essential modules in modern automotive electronics is the Body Control Module (BCM). The BCM is responsible for managing various systems such as headlights, taillights, fog lights, door locks, windows, etc.

The BCM works as a central hub, collecting data from multiple sensors located throughout the vehicle and sending commands to various electrical actuators and systems. When the BCM malfunctions, it can cause intermittent operation or complete failure of several vehicle systems, ultimately affecting the vehicle's overall performance. This article highlights the typical symptoms of a faulty BCM, helping identify potential problems and their underlying causes.

What Causes Body Control Module (BCM) Failures?

Physical Damage: Due to the BCM’s placement within the vehicle, it is subjected to continuous vibration. Over time, this ongoing mechanical strain can eventually result in the failure of BCM.

Liquid Damage: Liquid spillage or leaks can corrode the electronic components of the BCM, ultimately resulting in its failure.

Electrical Issues: Faulty wiring or an excessive number of aftermarket accessories in your vehicle can cause an excessive electrical load on the BCM. This, in turn, can overload the module, leading to malfunctions and failures.

Wear and Tear: Over time, the BCM's internal components can degrade due to normal wear and tear. Continuous operation, temperature fluctuations, and exposure to environmental factors can all contribute to the degradation of the BCM's components, leading to failure.

Common Symptoms of a Faulty Body Control Module (BCM)

Malfunction Indicator Light (MIL) or Check Engine Light (CEL) Illuminates

One of the most frequent indications of a malfunctioning BCM is the illumination of the MIL or other warning lights on the dashboard. The BCM communicates with systems such as the PCM, Supplemental Restraint System (SRS), and Anti-lock Braking System (ABS), giving it the ability to monitor their performance. If the BCM detects any issues, it will trigger the MIL to alert the driver.

To identify the exact reason the MIL is illuminated, use an OBD2 scan tool to retrieve the Diagnostic Trouble Codes (DTCs) and Freeze Frame data to determine the root of the issue. This will help you understand what has gone wrong and take the necessary steps to correct it.

Battery Drain

Although a small amount of parasitic drain is acceptable, a BCM malfunction can lead to an excessive drain. This can cause the battery to deplete rapidly, sometimes within hours. This draw occurs when the BCM incorrectly supplies power to a specific accessory at inappropriate times.

Abnormal Electrical Function

A faulty BCM can result in electrical malfunctions within a vehicle, manifesting as problems with headlights, taillights, and interior lights. Additionally, the BCM may contribute to issues with the vehicle's radio and other electronic systems.

Problems Starting the Vehicle

In certain instances, a vehicle with a non-operational or defective BCM may either fail to start altogether or initiate startup only to stall shortly afterward. A malfunctioning BCM may fail to recognize the transponder chip in the vehicle’s key or neglect to transmit a "start" signal from the vehicle's ignition switch, resulting in the inability to engage the starter.

Identify A Faulty Body Control Module (BCM) with the Innova Scan Tool

The Innova Scan Tool is an extremely beneficial diagnostic instrument designed to swiftly pinpoint issues within a vehicle’s systems. It is effective in identifying problems related to the BCM by retrieving DTCs associated with it. With an Innova Scan, you can retrieve existing DTCs, the I/M Status of the vehicle, and any Freeze Frame data stored in the vehicle’s computers. This tool effectively aids in the diagnosis of BCM-related issues in vehicles, helping you accurately identify and resolve problems with ease.

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