Quick Answer
U0399 means: U0399 indicates a communication failure between vehicle control modules.
Can I drive with U0399? Immediate attention is recommended to prevent further system failures.
Common Questions
What does U0399 mean and how does it affect my car?
The U0399 code signifies a communication failure between your vehicle's control modules, which can affect systems like the engine and transmission. This can lead to reduced performance, erratic behavior, and potential safety issues.
What are the most common causes of U0399 and how much does it cost to fix?
Common causes include damaged wiring (60% likelihood), malfunctioning BCM (25%), and corrosion at connectors. Repair costs range from $100 for wiring fixes to $600 for BCM replacement.
Can I drive my car with U0399 or should I stop immediately?
It's advisable to address the U0399 code as soon as possible. Driving with this code could lead to further damage and unsafe vehicle operation.
How can I diagnose U0399 myself using GeekOBD APP?
With the GeekOBD APP, you can scan for trouble codes, view real-time data, and check freeze frame data to understand the context of the U0399 code, leading you to potential fixes.
What vehicles are most commonly affected by U0399?
The U0399 code is frequently noted in models like the 2015-2018 Honda Civic, Toyota Camry, and certain Ford vehicles. Always check for recalls or technical service bulletins related to your model.
How can I prevent U0399 from happening again?
Regular maintenance of electrical connections, ensuring modules are updated, and periodic inspections can help prevent future occurrences of the U0399 code.
What is U0399?
The U0399 diagnostic trouble code (DTC) denotes a communication issue between control modules in your vehicle. Specifically, it means that there is a problem with the vehicle's communication network, preventing modules from sharing vital information. This code can appear in various vehicles but is commonly seen in models like the 2015-2018 Honda Civic, as well as some Toyota and Ford vehicles. When the U0399 code is triggered, it usually indicates that the vehicle's body control module (BCM) is unable to communicate effectively with other modules, such as the engine control module (ECM) or transmission control module (TCM). This can lead to various issues, including erratic behavior of vehicle systems, dashboard warning lights, and even reduced performance. Ignoring the U0399 code could lead to further complications, such as inconsistent engine performance or even safety issues if critical systems cannot communicate correctly. It’s essential for vehicle owners to address this code promptly to ensure that their vehicle operates smoothly and safely.
System: U - Network (Communication, CAN Bus)
Symptoms
Common symptoms when U0399 is present:
- Check engine light stays on constantly, indicating a communication fault.
- Engine performance may be erratic, such as stalling or hesitation during acceleration.
- Dashboard warning lights for various systems may illuminate, causing confusion for the driver.
- Inconsistent operation of features like power windows or door locks, which may stop responding.
- Fuel efficiency may decrease significantly, sometimes by as much as 10-15% depending on the severity of the issue.
Possible Causes
Most common causes of U0399 (ordered by frequency):
- The most common cause of U0399 is damaged wiring or connectors related to the communication network, with a likelihood of 60%. Inspecting wiring for wear is crucial.
- Another frequent cause is a malfunctioning body control module, where the BCM fails to process signals correctly, leading to a 25% chance of occurrence.
- Corrosion at connectors or ground points can also lead to communication failures; maintaining clean connections can help prevent this issue.
- Less common but serious causes include a software glitch that may require a factory reset or update, which is critical for newer vehicles equipped with complex software.
- A rare cause could be a complete failure of the control module, which would necessitate replacement and is typically the most expensive fix.
U0399 Repair Costs
Cost Breakdown by Repair Type
Wiring Repair
Repair or replace damaged wiring and connectors.
- Total: $100 - $300
- Success rate: 85%
BCM Replacement
Replace the malfunctioning body control module.
- Total: $300 - $600
- Success rate: 90%
Software Update
Update the vehicle's software to correct communication issues.
- Total: $150 - $250
- Success rate: 75%
Money-Saving Tips for U0399
- 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 U0399 Diagnosis Process
Follow these systematic steps to accurately diagnose U0399. Each step builds on the previous one to ensure accurate diagnosis.
Step 1: Step 1: Perform a visual inspection to look for damaged wiring, loose connectors, or corrosion, which may take about 5-10 minutes
Step 1: Perform a visual inspection to look for damaged wiring, loose connectors, or corrosion, which may take about 5-10 minutes.
Step 2: Step 2: Use an OBD2 scanner or the GeekOBD APP to retrieve all trouble codes and freeze frame data that provides context for the fault, usually taking 10-15 minutes
Step 2: Use an OBD2 scanner or the GeekOBD APP to retrieve all trouble codes and freeze frame data that provides context for the fault, usually taking 10-15 minutes.
Step 3: Step 3: Conduct component testing with a multimeter or diagnostic tool to check for proper voltage at the BCM and other related modules, which can take 20-30 minutes
Step 3: Conduct component testing with a multimeter or diagnostic tool to check for proper voltage at the BCM and other related modules, which can take 20-30 minutes.
Step 4: Step 4: After any repairs, perform a system function test to ensure proper operation and clear any stored codes, expected to take about 10-15 minutes
Step 4: After any repairs, perform a system function test to ensure proper operation and clear any stored codes, expected to take about 10-15 minutes.
Step 5: Step 5: Finally, conduct a road test to verify the repairs under various driving conditions, lasting about 15-20 minutes
Step 5: Finally, conduct a road test to verify the repairs under various driving conditions, lasting about 15-20 minutes.
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: BCM Replacement in a 2017 Honda Civic
Vehicle: 2017 Honda Civic, 45,000 miles
Problem: Customer reported check engine light and erratic electrical systems.
Diagnosis: Diagnostic scan revealed U0399 code, and visual inspection showed corrosion on wiring.
Solution: Replaced the body control module and cleaned all connectors.
Cost: $450 (part: $350, labor: $100)
Result: Post-repair, all systems functioned normally, and the check engine light was cleared.
Case Study 2: Wiring Repair in a 2016 Ford Fusion
Vehicle: 2016 Ford Fusion, 60,000 miles
Problem: Customer experienced intermittent power loss and dashboard lights.
Diagnosis: U0399 code was found, indicating a communication issue; further inspection revealed damaged wiring.
Solution: Repaired the damaged wiring harness connecting the BCM to other modules.
Cost: $200 (parts: $50, labor: $150)
Result: The vehicle's performance improved significantly, and no further issues were reported.