U0140: lost BCM communication. Shared body-function failures, supply, ground and connector checks before module replacement.
Meaning, symptoms, causes and checks
U0140 concerns missing messages from the body control module (BCM). Several body functions failing together may share a power, ground or communication problem. The code does not establish that the BCM needs replacement or that every affected window, lock or switch has failed.
Affected system: Control-module communication
Symptoms
- Intermittent body functions or warnings, such as cycling door locks.
- Depending on the vehicle, keyless/start functions can also be affected; a historical code may have no current symptom.
Possible causes
- Low supply voltage, loose battery connections or a poor BCM ground.
- Moisture/corrosion at BCM connectors, damaged data wiring or, after electrical checks, a module/software fault.
What to check
- Save a complete scan and list which body functions fail at the same time; distinguish current faults from history.
- Try direct BCM communication. If reachable, read its local supply and output faults rather than replacing every affected component.
- Verify battery and charging condition, BCM supplies and ground voltage drops under the exact OEM procedure.
- Inspect BCM connectors for moisture/corrosion and map related missing modules. A shared supply or network failure should be repaired before programming or replacement.
- After confirmed repair, retest communication and each originally affected function. Replacement BCMs can require vehicle-specific setup; U0140 alone is not a programming instruction.
Also written as: U0140-00, U014000, UO140 (some scan tools add the fault-type byte, e.g. -00).