What Is the U0140 U0140 Code: Lost Communication With Body Control Module (BCM)?

The U0140 diagnostic trouble code (DTC) indicates a lost communication problem with the Body Control Module (BCM). This means one or more vehicle control modules are unable to exchange data with the BCM through the vehicle communication network.

The Body Control Module is one of the most important electronic controllers in modern vehicles. It manages many body-related systems including lighting, door locks, windows, alarm systems, interior functions, and communication between different vehicle modules.

U0140 is a network communication fault and does not always mean that the BCM itself has failed. The problem may be caused by low battery voltage, damaged wiring, CAN Bus communication issues, connector problems, blown fuses, or another module affecting the network.

What Does the Body Control Module (BCM) Do?

The BCM acts as a central controller for many vehicle electrical functions. It receives information from switches and sensors, processes commands, and communicates with other modules through the CAN network.

When communication with the BCM is interrupted, multiple systems may be affected because many modules depend on BCM messages.

BCM Function	Possible Effect When Communication Is Lost
Exterior Lighting	Lights may not operate correctly
Door Lock System	Remote locking problems
Interior Electronics	Cabin functions may fail
Security System	Alarm or immobilizer issues

How U0140 Communication Failure Happens

The BCM communicates by sending and receiving digital messages through the vehicle network. If the communication path is interrupted, other modules cannot receive BCM information and store U0140.

BCM Power Supply
↓ BCM Internal Operation
↓ CAN Communication Network
↓ Communication Interruption
↓ Lost BCM Communication
↓ U0140 Stored

Typical BCM Pinout Example

Circuit	Function
B+	Battery Power Supply
Ground	BCM Ground Circuit
CAN High	Network Communication +
CAN Low	Network Communication -

Note: BCM connector locations, pin numbers, and wire colors are different between manufacturers and models. Always verify the correct wiring diagram before testing.

Common Symptoms of U0140

When communication with the Body Control Module (BCM) is lost, many electrical systems may be affected. The symptoms depend on the vehicle design and which systems depend on BCM communication.

Symptom	Description
Multiple Warning Lights	Several systems may display communication warnings.
Power Door Lock Problems	Remote locking or door functions may stop working.
Lighting Problems	Exterior or interior lights may operate incorrectly.
Security System Issues	Alarm or immobilizer functions may be affected.
Scan Tool Cannot Access BCM	No communication with the BCM module.
Intermittent Electrical Failures	Systems fail and return randomly.

Possible Causes of U0140

U0140 can be caused by problems with BCM power supply, communication wiring, connectors, network modules, or the BCM itself.

Cause	Explanation
Weak Battery Voltage	Low voltage can cause modules to shut down or reset.
Blown BCM Fuse	The BCM loses its power supply.
CAN Bus Open Circuit	Communication path is interrupted.
CAN Bus Short Circuit	Network signals become corrupted.
Corroded Connectors	Creates high resistance and unstable communication.
Faulty Gateway Module	Prevents communication between networks.
Failed BCM	Internal BCM failure stops communication.

U0140 Diagnostic Procedure

A correct diagnosis starts with checking communication, power supply, and network wiring before replacing the BCM.

Complete Vehicle Scan ↓ Record All U-Codes ↓ Check Battery Voltage ↓ Verify BCM Power & Ground ↓ Inspect CAN Wiring ↓ Test Network Communication ↓ Isolate Faulty Module ↓ Repair & Verify

Step 1: Scan All Modules

Use an advanced scan tool to identify which modules communicate and which modules are offline. Save all fault codes before clearing them.

Step 2: Check BCM Power and Ground

Verify battery voltage, ignition power, and ground circuits at the BCM connector. A missing power or ground supply can create a false communication fault.

Step 3: Test CAN Bus Network

Inspect CAN High and CAN Low circuits for open circuits, shorts, corrosion, or damaged wiring.

Step 4: Isolate Network Problems

Disconnect suspected modules one at a time to determine whether a faulty module is preventing BCM communication.

Electrical Testing (Typical Values)

Test	Typical Result
Battery Voltage	12.0–14.8 V
CAN Bus Resistance	Approximately 60 Ω
CAN High Voltage	Approximately 2.5–3.5 V
CAN Low Voltage	Approximately 1.5–2.5 V

Live Data Analysis for U0140

Live Data analysis helps determine whether the Body Control Module (BCM) is communicating correctly with other vehicle modules. Since U0140 is a communication fault, technicians should focus on module status, network activity, and message availability.

When U0140 is active, the scan tool may show the BCM as unavailable, missing data messages, or multiple communication errors from other modules.

Live Data Parameter	Normal Condition	U0140 Fault Condition
BCM Communication Status	Online / Responding	No Communication
Network Health	Stable Data Exchange	Communication Errors
BCM Voltage Status	Stable Power Supply	Low Voltage / Reset
Gateway Module Status	Connected	BCM Missing

Oscilloscope Testing for U0140

An oscilloscope is one of the best tools for diagnosing BCM communication problems. It allows technicians to see the actual CAN Bus waveform and identify missing or distorted communication signals.

Normal CAN Bus Communication Waveform

CAN High
__|‾|__|‾|__|‾|__|‾|__
CAN Low
‾|__|‾|__|‾|__|‾|__
✓ Normal Digital Communication

CAN Communication Missing

CAN Network Signal
_________________
✗ No Communication Activity

Intermittent BCM Communication Fault

CAN Signal:
__|‾|_____|‾|____|__
⚠ Signal Drops During Movement Or Vibration

BCM Communication Signal Flow

Vehicle Control Modules
↓
CAN Communication Network
↓
Gateway Module
↓
BCM Network Lines
↓
Body Control Module
↓
Lighting / Doors / Security Systems

Common Diagnostic Mistakes

Replacing the BCM without checking power and ground circuits.
Assuming every U0140 code means the BCM is defective.
Ignoring battery voltage problems.
Not checking CAN Bus resistance and wiring integrity.
Failing to inspect connectors for corrosion or moisture.
Using incorrect network diagrams from different vehicle models.
Ignoring aftermarket devices connected to the communication network.

Common Repairs for U0140

The correct repair for U0140 depends on the source of the communication failure. A complete diagnostic process should be completed before replacing the Body Control Module (BCM).

Repair damaged CAN High or CAN Low communication wiring.
Repair corroded or loose BCM connector terminals.
Restore BCM power supply and ground circuits.
Replace blown fuses related to the BCM system.
Repair damaged wiring harness sections.
Repair or replace a faulty Gateway Module if network communication is affected.
Replace and program the BCM if internal failure is confirmed.
Clear all communication codes and verify normal operation after repair.

Estimated Repair Cost

The repair cost for U0140 depends on whether the problem is a simple wiring fault or a failed electronic control module.

Repair Type	Estimated Cost
Diagnostic Scan	$80–200
BCM Connector Repair	$50–150
CAN Wiring Repair	$100–400
Gateway Module Repair	$300–900
BCM Replacement & Programming	$400–1200+

Recommended Diagnostic Tools

Diagnosing U0140 requires tools capable of checking communication networks, electrical circuits, and module operation.

Advanced Scan Tool: Reads communication codes and checks BCM availability.
Digital Multimeter: Tests voltage, ground, continuity, and resistance.
Oscilloscope: Displays CAN Bus waveform activity.
Wiring Diagram Software: Provides BCM connector and network routing information.
Back Probe Kit: Allows safe testing of module circuits.
Terminal Repair Tools: Repairs damaged connector pins.

Related DTC Codes

Related communication codes connected with BCM and vehicle network faults:

U0131 Code - Lost Communication With Power Steering Control Module
U0141 Code - Lost Communication With Body Control Module B
U0155 Code - Lost Communication With Instrument Panel Cluster
U0100 Code - Lost Communication With ECM/PCM
U0121 Code - Lost Communication With ABS Control Module
U0073 Code - Control Module Communication Bus Off

Frequently Asked Questions (FAQ)

What does U0140 mean?

U0140 means the vehicle has lost communication with the Body Control Module (BCM).

Can U0140 stop the vehicle from starting?

In some vehicles, yes. If the BCM controls security or authorization functions, communication loss may prevent starting.

Does U0140 mean the BCM is bad?

No. The fault may be caused by wiring problems, power supply issues, network faults, or another module affecting communication.

Can a dead battery cause U0140?

Yes. Low voltage during starting or battery failure can cause temporary communication loss between modules.

How do I fix U0140 permanently?

The permanent repair requires identifying the exact communication failure, repairing the electrical problem, and confirming that the BCM communicates normally.

Related Sections

U Code
Acronyms
Live Data
Sensors
Dashboard Warning

Conclusion

The U0140 diagnostic trouble code indicates a communication failure with the Body Control Module. Because the BCM controls many important vehicle functions, accurate diagnosis is required before replacing any module.

Checking power supply, ground circuits, CAN Bus wiring, connectors, and network signals provides the most reliable way to identify the cause. Proper diagnosis reduces repair costs and prevents unnecessary electronic module replacement.

OBD Spark provides automotive diagnostic guides covering OBD-II trouble codes, CAN Bus communication, electronic modules, and professional repair procedures.

OBD Spark

Search This Blog

U0140 Code: Lost Communication With Body Control Module (BCM)