U0140 code definition and possible causes

U0140 Lost Communication With Body Control Module

A U0140 code is a generic (not manufacturer-specific)

Body Control Module

data network-related trouble code.  It is defined as: Lost Communication with Body Control Module (BCM). In lay language, that means the digital network can’t communicate with the body control module.

A body control module (BCM) is an electronic control unit found in modern vehicles that manages various body-related functions and systems. It acts as a centralized computer that controls and monitors several convenience, safety, and security features in the vehicle.

Most common causes of a U0140 code

Wiring Issues
Damaged, shorted, or open wiring anywhere on the data bus can cause this trouble code. This could be due to chafed or pinched wires, corrosion, or other physical damage.

Other Module Faults
Problems with other control modules that communicate along the same data bus as the BCM can cause this trouble code to set. For example, since the BCM communicates with the instrument cluster, a short in the cluster can sometimes cause the U0140 code to be set.

Loose or Corroded Connectors
Loose or corroded connectors in the BCM circuit can lead to intermittent or poor electrical connections, resulting in communication failures.

Faulty Body Control Module (BCM)
The BCM itself may be defective or malfunctioning, causing communication issues with other modules or systems.

Power or ground issues to the BCM
If the BCM is not receiving proper power supply voltage, it may not function correctly and communicate with other modules, setting the U0140 code.

Software or Firmware Issues
In some cases, the BCM may have outdated or corrupted software or firmware, leading to communication failures and triggering the U0140 code.

How to diagnose a U0140 code

1) Start by checking for good power and ground to the BCM
2) Next, remove the connectors to the BCM and check for signs of corrosion. Repair if necessary.
3) Locate a wiring diagram and identify all other modules that share that same data bus. Remove each module, one at a time, to see if communication to the BCM restores itself. If removing a module results in good BCM communication, then the problem is in the unplugged module.
4) If removing modules doesn’t enable communication, then the BCM is most likely bad. However, check for service bulletin updates before replacing.
5) Also, check for online BCM rebuilders and check the options for refurbishing yours rather than buying a new unit.

What does the BCM do?

Keyless Entry/Remote Keyless Entry
The BCM controls the locking and unlocking of doors, trunk/liftgate, and other access points in response to signals from the key fob or remote control.

Interior Lighting
It manages the operation of interior lights, such as dome lights, map lights, and courtesy lights, based on door open/close status, ignition state, and other inputs.

Power Windows/Sunroof
The BCM controls the operation of power windows, including anti-pinch protection, and also manages the power sunroof or moonroof, if equipped.

Power Door Locks
It controls the locking and unlocking of doors, either automatically (based on vehicle speed or other conditions) or manually (via switch inputs).

Exterior Lighting
The BCM may control exterior lighting functions, such as headlights, taillights, turn signals, and hazard lights.

Security System
It manages the vehicle’s security system, including the alarm, immobilizer, and theft-deterrent functions.

Chime/Warning Indicators
The BCM generates audible chimes or warnings for various events, such as open doors, low fuel, or seatbelt reminders.

Wiper/Washer Systems
It can control the operation of windshield wipers, rear wipers, and washer fluid pumps.

Instrumentation
In some vehicles, the BCM may interact with the instrument cluster to display certain warning lights or messages.

© 2012 Rick Muscoplat