U021B - Communication Issue with the Battery Energy Control Module (BECM) in Honda Accord and Ford Fusion

Quick Answer

U021B means: DTC U021B indicates a communication failure between the Engine Control Module and the Battery Energy Control Module.

Fix: Check and replace faulty components Cost: $150 - $400 Time: 90-180 minutes

Can I drive with U021B? Immediate attention is required to prevent further damage.

Common Questions

What does U021B mean and how does it affect my car?

DTC U021B signifies a communication breakdown between your vehicle’s Engine Control Module and the Battery Energy Control Module. This can cause performance issues like hesitation during acceleration, decreased fuel economy, and may even lead to a limp mode condition, where your car limits speed and power to protect itself. Addressing this code is essential to maintain your car's efficiency and functionality.

What are the most common causes of U021B and how much does it cost to fix?

Common causes of U021B include faulty wiring (60% likelihood), software glitches, and battery issues. Repair costs can range from $150 for wiring repairs to $1,500 for complete module replacements, depending on the severity and nature of the issue.

Can I drive my car with U021B or should I stop immediately?

While it may be tempting to continue driving, it’s not advisable. DTC U021B indicates a serious communication issue that can lead to engine performance problems. Continuing to drive could exacerbate the problem, leading to more costly repairs.

How can I diagnose U021B myself using GeekOBD APP?

Using the GeekOBD APP, you can scan your vehicle for trouble codes and access freeze frame data to understand the conditions when U021B appeared. Look for related codes that may provide additional context and perform a visual inspection of wiring and connectors.

What vehicles are most commonly affected by U021B?

DTC U021B is frequently seen in hybrid models such as the 2010-2015 Honda Accord Hybrid and the 2013-2018 Ford Fusion Hybrid. If you own one of these vehicles, be vigilant for symptoms related to this code.

How can I prevent U021B from happening again?

Regular maintenance, including battery checks and ensuring that electrical connections are clean and secure, can help prevent U021B. Additionally, keeping your vehicle’s software updated can help avoid communication issues.

What is U021B?

The DTC U021B diagnostic trouble code indicates that there is a communication issue between the vehicle's Engine Control Module (ECM) and the Battery Energy Control Module (BECM). This problem often arises in hybrid vehicles, particularly in models like the 2010-2015 Honda Accord Hybrid and the 2013-2018 Ford Fusion Hybrid. When the ECM fails to receive vital information from the BECM, it may lead to performance issues and reduced fuel efficiency. Additionally, the vehicle may exhibit symptoms such as the check engine light illuminating and, in some cases, it may enter 'limp mode' for safety. This situation can arise due to faulty wiring, bad connectors, or even software glitches in the control modules. Ignoring this code can lead to more severe issues, including battery and engine performance degradation over time. Therefore, it's crucial for vehicle owners to address this code promptly to ensure optimal vehicle performance and longevity.

System: U - Network (Communication, CAN Bus)

Symptoms

Common symptoms when U021B is present:

  • Check engine light stays on constantly, which may indicate ongoing communication issues that need to be resolved.
  • Engine hesitates during acceleration, causing a lack of power and responsiveness when you press the accelerator.
  • Fuel economy decreased by 10-15%, which can significantly affect your wallet over time.
  • Inconsistent electrical system performance, including issues with dashboard lights and infotainment systems.
  • The vehicle may enter 'limp mode,' restricting speed and power to protect the engine from further damage.

Possible Causes

Most common causes of U021B (ordered by frequency):

  1. Faulty wiring or connectors between the ECM and BECM is the most common cause, with a likelihood of around 60%. Damaged wires can disrupt communication.
  2. Software glitches or outdated firmware in the ECM or BECM can cause communication failure, requiring a software update or reprogramming.
  3. A weak or failing battery may also lead to issues in communication, as the modules rely on stable power to function correctly. Regular battery maintenance can help prevent this.
  4. Less common but serious causes include physical damage to the control modules due to water intrusion or extreme temperatures, which can lead to extensive damage.
  5. Rare but possible causes include interference from aftermarket electronics that disrupt the communication network within the vehicle.

U021B Repair Costs

Cost Breakdown by Repair Type

Wiring Repair or Replacement

Repairing or replacing damaged wiring and connectors between the ECM and BECM.

  • Total: $150 - $400
  • Success rate: 85%
ECM or BECM Reprogramming

Updating the software of the engine or battery control module to eliminate glitches.

  • Total: $100 - $250
  • Success rate: 75%
Complete Module Replacement

Replacing either the ECM or BECM if they are confirmed to be defective.

  • Total: $500 - $1,500
  • Success rate: 90%
Money-Saving Tips for U021B
  • Start with the most common and least expensive repairs first
  • Use GeekOBD APP to confirm diagnosis before replacing expensive parts
  • Consider preventive maintenance to avoid future occurrences
  • Compare prices for OEM vs aftermarket parts based on your needs
  • Address the issue promptly to prevent more expensive secondary damage

Diagnostic Steps

Professional U021B Diagnosis Process

Follow these systematic steps to accurately diagnose U021B. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion around the BECM and ECM (5-10 minutes)

Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion around the BECM and ECM (5-10 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context and history (10-15 minutes)

Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context and history (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 3: Step 3: Component testing - Use a multimeter to test the voltage and ground signals at the BECM and ECM to ensure they are functioning properly (20-30 minutes)

Step 3: Component testing - Use a multimeter to test the voltage and ground signals at the BECM and ECM to ensure they are functioning properly (20-30 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 4: Step 4: System function test - Verify the operation of the BECM by checking the battery's performance and ensuring that communication is restored post-repair (10-15 minutes)

Step 4: System function test - Verify the operation of the BECM by checking the battery's performance and ensuring that communication is restored post-repair (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and ensure no new codes appear (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and ensure no new codes appear (15-20 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.

Important Notes

  • Always verify the repair with GeekOBD APP after completing diagnostic steps
  • Clear codes and test drive to ensure the problem is resolved
  • Address underlying causes to prevent code recurrence

Real Repair Case Studies

Case Study 1: 2014 Honda Accord Hybrid Communication Repair

Vehicle: 2014 Honda Accord Hybrid, 75,000 miles

Problem: Customer reported the check engine light was on, and the vehicle was experiencing hesitation during acceleration.

Diagnosis: Using the GeekOBD APP, the technician confirmed a U021B code. A visual inspection revealed damaged wiring near the BECM.

Solution: Repaired the wiring and reconnected the ECM, after which the check engine light was cleared.

Cost: $250 (including parts and labor)

Result: Post-repair, the vehicle ran smoothly, and the check engine light did not reappear during a follow-up test drive.

Case Study 2: 2016 Ford Fusion Hybrid Module Replacement

Vehicle: 2016 Ford Fusion Hybrid, 60,000 miles

Problem: Check engine light on, with no power to the infotainment system.

Diagnosis: Diagnostic testing revealed a U021B code. The BECM was found to be non-responsive during testing.

Solution: Replaced the BECM and updated the software to restore communication.

Cost: $1,200 (parts and labor for module replacement)

Result: After the repair, the vehicle's electrical systems functioned normally, and the customer was satisfied with the resolution.

Diagnose U021B

Use GeekOBD APP for professional diagnosis!

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  • Professional-grade analysis
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Code Information

Code: U021B
System: Network (Communication, CAN Bus)
Severity: HIGH
Category: Network Codes