U0140 Code: Lost Communication With Body Control Module – OBDII/EOBD Guide

In the realm of automotive diagnostics, trouble code U0140 signals a critical issue: “Lost Communication With Body Control Module.” This OBD-II/EOBD code, while generic to all makes and models from 1996 onwards, necessitates a systematic approach to troubleshooting. As a content creator for autelfrance.com, and an automotive repair expert, this guide aims to provide a comprehensive understanding of the U0140 code, its implications, symptoms, potential causes, and diagnostic procedures, optimized for an English-speaking audience seeking in-depth information and SEO relevance.

Understanding the U0140 Code: Lost Communication with BCM

The Body Control Module (BCM) is a pivotal electronic control unit within a vehicle’s electrical network. It orchestrates a wide array of functions beyond just engine management, encompassing convenience and safety systems. These functions include, but aren’t limited to:

• Tire Pressure Monitoring System (TPMS)
• Remote Keyless Entry
• Power Door Locks
• Anti-theft Alarm System
• Heated Mirrors
• Rear Window Defroster
• Front and Rear Windshield Washers and Wipers
• Horn

Furthermore, the BCM interfaces with various input signals from components like seat belt sensors, ignition switch, door ajar indicators, parking brake, cruise control system, engine oil level sensor, and even window washer/wiper controls. It also plays a role in battery rundown protection, temperature sensing, and low power mode operation. Therefore, any malfunction, loose connection, or wiring issue affecting the BCM can disrupt numerous vehicle functionalities.

Code U0140 specifically indicates a communication breakdown. It signifies that the Engine Control Module (ECM) has lost communication with the BCM. This fault could stem from issues within the BCM itself, the wiring harness connecting the BCM, or a disruption in the Controller Area Network (CAN) communication line that facilitates data exchange between the BCM and ECM. It’s important to note that U0140 shares similarities with related codes such as U0141, U0142, U0143, U0144, and U0145, often pointing towards similar communication network problems within different modules.

Image alt: Body Control Module (BCM) unit, a key component in modern vehicle electronics, often located within the passenger compartment.

Symptoms of a U0140 Code

The most immediate indication of a U0140 code is the illumination of the Malfunction Indicator Light (MIL), commonly known as the check engine light. This signals that the ECM has detected and stored a diagnostic trouble code. Beyond the warning light, drivers may experience a range of symptoms related to the BCM’s compromised functionality. The severity and type of symptoms often depend on the exact nature of the problem – whether it’s a wiring fault, BCM failure, or communication interruption.

Common symptoms associated with a U0140 code may include:

• Check Engine Light is On: The most direct indicator that a fault has been detected by the vehicle’s computer system.
• Malfunctioning Body Control Systems: This is the most noticeable symptom. Expect issues with features controlled by the BCM, such as power windows, door locks, interior lighting, wipers, and security systems. Some or all of these systems might operate erratically or cease functioning altogether.
• Engine Performance Issues (Less Common): In some cases, a U0140 code can be accompanied by engine performance problems. These may manifest as:
  • Misfiring at High Speeds: Engine stumbles or hesitates, particularly at higher velocities.
  • Vehicle Shaking at Higher Speeds: Unusual vibrations felt as speed increases.
  • Poor Acceleration: Engine responsiveness is diminished; the vehicle feels sluggish during acceleration.
  • Vehicle May Not Start: In severe cases, communication issues can prevent the vehicle from starting.
• Blown Fuses: Repeatedly blown fuses in circuits related to the BCM or its controlled systems might indicate a short circuit contributing to the communication problem.

Potential Causes Behind a U0140 Code

Several factors can lead to a U0140 code. Understanding these potential causes is crucial for effective diagnosis and repair. The issues generally fall into categories of physical damage, electrical faults, or component failure:

• BCM Damage from Impact: In vehicle collisions or incidents involving significant jarring, the BCM itself can be physically damaged. The impact force can cause internal component failure within the module or dislodge connectors and wiring.
• Wiring Harness Damage: The wiring harness connecting to the BCM is vulnerable to damage.
  • Loose Connections: Connectors can become loose due to vibration or accidental disturbance, interrupting electrical signals.
  • Corrosion: Moisture and environmental exposure can lead to corrosion within connectors and wiring, increasing resistance and hindering signal transmission.
  • Exposed or Cut Wires: Abrasion, physical damage, or rodent intrusion can expose проводники or sever wires within the harness, causing open circuits or short circuits.
• Short Circuits: Exposed wiring can make contact with other wires or metallic vehicle components, creating short circuits. Shorts can disrupt BCM operation and potentially damage the module or related circuits.
• Heat Damage: Excessive heat from the engine compartment or fire-related incidents can damage the BCM or melt the insulation on the wiring harness. Heat-damaged wiring can lead to shorts or open circuits.
• Water Damage: Water intrusion into the BCM or its connectors can cause corrosion, short circuits, and module failure. Flooding or water leaks are common culprits.
• Excessive Vibration: Prolonged exposure to excessive vibration, perhaps from unbalanced tires or failing engine mounts, can contribute to wear and tear on the BCM and its connections over time, eventually leading to failure.
• BCM Component Failure: Like any electronic component, the BCM can fail due to age, internal defects, or stress. Simple wear and tear over the vehicle’s lifespan can lead to internal malfunctions within the module.

Diagnostic and Repair Steps for U0140

Diagnosing a U0140 code requires a systematic approach, starting with basic checks and progressing to more in-depth electrical testing. Here’s a step-by-step guide for technicians:

1. Preliminary Checks & TSBs:

   • Technical Service Bulletins (TSBs): Before commencing any diagnostic work, always consult vehicle-specific TSBs. Manufacturers often issue bulletins for known issues and recommended solutions. A TSB related to the BCM or U0140 code for the specific vehicle model can save significant diagnostic time.
   • Locate the BCM: Refer to the vehicle’s repair manual to pinpoint the BCM’s location. BCM placement varies significantly across vehicle makes and models.

2. Symptom Verification & Fuse Inspection:

   • Document Symptoms: Carefully note all malfunctioning systems. This list helps narrow down whether the issue is BCM-related and can guide further diagnosis.
   • Fuse Check: Always begin with fuse inspection. Check fuses and relays associated with the BCM and the non-functional systems identified in the symptom verification step. A blown fuse is a common cause of electrical malfunctions and is a simple fix.

3. Visual Inspection of BCM and Wiring:

   • Connector Inspection: Visually examine the BCM connectors.
     • Security: Ensure connectors are firmly seated and locked in place. Gently wiggle connectors to check for looseness.
     • Corrosion: Look for signs of corrosion on connector terminals. Corrosion can impede electrical conductivity.
     • Pin Integrity: Inspect connector pins for damage, bending, or breakage.
   • Wiring Harness Inspection: Trace the wiring harness connected to the BCM.
     • Damage: Look for any signs of physical damage to the harness, such as cuts, abrasions, or melted insulation.
     • Routing: Check if the harness is properly routed and secured, away from sharp edges or heat sources.

4. Power and Ground Testing at BCM:

   • Diagnostic Code Reader: Utilize a diagnostic scan tool capable of reading BCM data. This tool can help identify specific pins or circuits that are not receiving power or ground.
   • Power and Ground Verification: Using a multimeter, systematically check for proper power and ground at the BCM connector pins as specified in the vehicle’s wiring diagram.
     • No Power: If power is absent at specific terminals, trace the wiring back to the power source, checking for open circuits or blown fuses along the way.
     • No Ground: Similarly, if ground is missing, trace the ground circuit to the vehicle’s chassis ground point, checking for open circuits or loose connections.

5. CAN Communication Line Testing:

   • CAN Bus Diagnostics: If power and ground are confirmed at the BCM, and communication is still lost, investigate the CAN communication lines. A CAN bus diagnostic tool or oscilloscope can be used to analyze CAN signal integrity and activity.
   • Wiring Integrity: Check the CAN bus wiring for continuity, shorts to ground, and shorts to voltage.

6. BCM Replacement (Last Resort):

   • Professional Opinion: Before replacing the BCM, consult with a dealership technician or experienced automotive electrician. BCM replacement often requires programming or configuration with specialized scan tools to integrate the new module with the vehicle’s systems.
   • BCM Programming: New BCMs typically need to be programmed to match the vehicle’s VIN and options. This programming step is crucial for proper BCM function and overall vehicle operation.

Tips for Addressing a U0140 Code

• Professional Programming: BCM replacement often necessitates programming. Ensure that replacement BCMs are correctly programmed using appropriate diagnostic equipment, typically available at dealerships or specialized repair shops.
• Burned Connector Signs: If BCM connectors exhibit signs of burning or melting, carefully inspect both the wiring harness and the BCM for damage. This often indicates a short circuit or excessive current draw.
• Unusual Odors: A burnt or unusual smell emanating from the BCM area is a strong indicator of internal BCM failure. Replacement is usually necessary in such cases.
• Tracing Wiring Harness Opens: If power is absent at the BCM, systematically trace the wiring harness to locate open circuits. Pay close attention to areas where the harness might be chafed, pinched, or exposed to heat.
• Partial BCM Failure: Remember that BCMs are complex modules. Partial failure is possible, where some functions operate correctly while others are impaired. Symptom observation is key to understanding the extent of the problem.

Disclaimer: This information is for informational purposes only and should not be considered professional repair advice. Automotive repair should be performed by qualified technicians. We are not liable for any actions taken based on this information.