Introduction:

The diagnostic trouble code (DTC) U0117, "Lost Communication With Brake Control Module," indicates a failure in the Controller Area Network (CAN) bus communication between the vehicle's electronic control units (ECUs), specifically impacting the Brake Control Module (BCM). This communication breakdown can lead to various issues, affecting braking performance and safety systems. Understanding the causes, symptoms, and troubleshooting steps for U0117 is crucial for accurate diagnosis and effective repair, ensuring the vehicle's braking system functions correctly and safely.

U0117: Comprehensive Overview

| Category | Description | Potential Impact everything

Detailed Explanations

DTC Code: U0117 is a standardized OBD-II diagnostic trouble code. This means it applies to all makes and models of vehicles equipped with the OBD-II system. The "U" indicates a network communication code, "0117" specifies the specific module that is having communication issues (Brake Control Module).

Lost Communication: This signifies that other modules on the vehicle's Controller Area Network (CAN) bus are unable to reliably communicate with the BCM. The CAN bus is a complex network that allows various ECUs (Engine Control Unit, Transmission Control Unit, ABS, etc.) to share data and coordinate functions. A loss of communication means the BCM is either not transmitting data, not receiving data, or the data being transmitted is corrupted.

Brake Control Module (BCM): The BCM is responsible for managing various braking functions, including Anti-lock Braking System (ABS), Traction Control System (TCS), Electronic Stability Control (ESC), and other related systems. Without proper communication, these systems may become disabled or malfunction, impacting vehicle safety. The BCM receives information from wheel speed sensors, steering angle sensors, and other inputs to determine the optimal braking strategy for various driving conditions.

Causes of U0117: Several factors can lead to a U0117 code:

  • Faulty BCM: The BCM itself may be failing due to internal component issues, corrosion, or electrical damage. This is often the most serious cause, requiring replacement of the module.
  • Wiring Issues: Damaged, corroded, or loose wiring harnesses or connectors related to the BCM can interrupt communication. This includes the power supply, ground connections, and the CAN bus wires.
  • CAN Bus Problems: Issues within the CAN bus network, such as shorts, open circuits, or excessive resistance, can disrupt communication between modules. This can be caused by damaged wiring, faulty connectors, or even a failing module on the bus that is disrupting the overall network.
  • Power Supply Issues: Insufficient voltage or a poor ground to the BCM can prevent it from functioning correctly and communicating with other modules.
  • Software Issues: In rare cases, a software glitch or corruption within the BCM's programming can cause communication problems.
  • Other Module Interference: A faulty module on the CAN bus may be sending out erroneous data, disrupting the communication of other modules, including the BCM.

Symptoms of U0117: The symptoms of a U0117 code can vary, but common indicators include:

  • ABS Warning Light: The Anti-lock Braking System (ABS) warning light will typically illuminate on the dashboard.
  • Traction Control Light: The Traction Control System (TCS) light may also illuminate.
  • Stability Control Light: The Electronic Stability Control (ESC) light could illuminate.
  • Disabled Braking Features: ABS, TCS, and ESC may be disabled or operating erratically.
  • Hard Braking: The vehicle may exhibit hard or jerky braking behavior.
  • Loss of Traction: Reduced traction control can lead to wheel spin or skidding, especially in slippery conditions.
  • Other Warning Lights: Other warning lights related to braking systems may also appear.
  • Difficulty Starting: In some cases, a communication problem can affect other vehicle systems, leading to difficulty starting.
  • Erratic Gauge Readings: Instrument cluster gauges may display incorrect or erratic readings.

Troubleshooting U0117: Diagnosing and repairing a U0117 code requires a systematic approach:

  1. Scan for Codes: Use an OBD-II scanner to confirm the presence of the U0117 code and any other related codes.
  2. Inspect Wiring: Carefully inspect the wiring harness and connectors associated with the BCM for any signs of damage, corrosion, or loose connections. Pay close attention to the CAN bus wires (typically twisted pairs).
  3. Check Power and Ground: Verify that the BCM is receiving adequate voltage and has a solid ground connection. Use a multimeter to check the voltage at the BCM power supply and ground terminals.
  4. CAN Bus Testing: Use a CAN bus diagnostic tool or multimeter to test the integrity of the CAN bus network. Check for shorts, open circuits, and proper resistance values. The CAN bus wires should typically have a resistance of around 60 ohms when measured between the CAN high and CAN low wires with the battery disconnected.
  5. BCM Testing: If possible, use a specialized scan tool to test the BCM's functionality and communication capabilities. This may involve performing output tests or reading live data from the module.
  6. Module Isolation: Disconnect other modules on the CAN bus one at a time to see if the U0117 code clears. This can help identify a faulty module that is disrupting communication.
  7. BCM Replacement: If all other troubleshooting steps fail, the BCM itself may be faulty and require replacement.
  8. Programming: After replacing the BCM, it will likely need to be programmed to the vehicle using a factory scan tool or a compatible aftermarket tool. This ensures the BCM is configured correctly and can communicate with other modules.

Common Mistakes:

  • Replacing the BCM without proper diagnosis: Replacing the BCM without thoroughly investigating the wiring, power supply, and CAN bus network can lead to misdiagnosis and unnecessary expense.
  • Ignoring related codes: The U0117 code may be accompanied by other codes that provide valuable clues about the underlying problem. Ignoring these codes can lead to an incomplete diagnosis.
  • Using incorrect diagnostic tools: Using generic OBD-II scanners that lack advanced CAN bus testing capabilities can hinder the troubleshooting process.

Frequently Asked Questions:

  • What does U0117 mean? U0117 indicates a "Lost Communication With Brake Control Module" error, meaning other vehicle modules can't reliably communicate with the BCM. This disrupts braking system functions.

  • Can I drive with a U0117 code? Driving with a U0117 code is not recommended, as it can affect braking performance and safety systems like ABS and TCS. Get it checked by a mechanic as soon as possible.

  • What are the common causes of U0117? Common causes include a faulty BCM, wiring issues, CAN bus problems, power supply issues, or software glitches. A thorough diagnosis is needed.

  • How do I fix a U0117 code? Fixing it involves inspecting wiring, checking power and ground, testing the CAN bus, and possibly replacing and programming the BCM. Professional diagnosis is recommended.

  • Is U0117 an expensive repair? The cost can vary depending on the cause. Replacing the BCM can be expensive, while wiring repairs are usually less costly.

Conclusion:

The U0117 code signals a critical communication failure affecting the Brake Control Module and potentially compromising vehicle safety. Accurate diagnosis, involving thorough inspection of wiring, power supply, and CAN bus integrity, is essential before considering BCM replacement. Consulting a qualified mechanic with experience in CAN bus diagnostics is highly recommended for efficient and effective repair.