Quick Answer
U0856 means: U0856 is a communication error between vehicle control modules, often leading to performance issues.
Can I drive with U0856? Immediate attention is advised to prevent further electronic failures.
Common Questions
What does U0856 mean and how does it affect my car?
U0856 indicates a communication problem between control modules, which can lead to poor engine performance and malfunctioning electronic features. If ignored, it can escalate into more serious issues.
What are the most common causes of U0856 and how much does it cost to fix?
Common causes include a faulty BCM, damaged wiring, or a failing PCM. Repair costs can range from $150 for wiring repairs to $800 for BCM replacement, depending on the severity of the issue.
Can I drive my car with U0856 or should I stop immediately?
While you may be able to drive with the U0856 code, it's advisable to limit driving until the issue is resolved to avoid further damage or safety risks.
How can I diagnose U0856 myself using GeekOBD APP?
Using the GeekOBD APP, perform an OBD2 scan to retrieve codes and inspect freeze frame data. Look for patterns in symptoms and consider checking wiring and connectors for damage.
What vehicles are most commonly affected by U0856?
The U0856 code is commonly found in models like the 2015-2018 Chevrolet Silverado and GMC Sierra, as well as some other GM vehicles from this era.
How can I prevent U0856 from happening again?
Regular vehicle maintenance, including inspections of wiring and connectors, software updates for modules, and addressing any electrical issues promptly, can help prevent the recurrence of U0856.
What is U0856?
The diagnostic trouble code (DTC) U0856 indicates a communication error between the vehicle's control modules. This code is particularly common in vehicles like the 2015-2018 Chevrolet Silverado and GMC Sierra. When the vehicle's various electronic control units (ECUs) cannot communicate effectively, it can lead to a host of issues, including poor engine performance, erratic behavior of electronic features, and even complete system failure in some cases. The U0856 code typically signifies that the Body Control Module (BCM) is having trouble communicating with one or more other modules in the vehicle, which may include the Powertrain Control Module (PCM), Transmission Control Module (TCM), or others. The underlying causes can range from simple issues like loose connectors or damaged wiring to more complex problems such as failing control modules. Ignoring this code can lead to significant performance issues and even safety risks, making it important for vehicle owners to address it promptly. If you're experiencing electronic malfunctions, erratic dashboard readings, or warning lights, this code may be the culprit, and immediate action is recommended to prevent further damage.
System: U - Network (Communication, CAN Bus)
Symptoms
Common symptoms when U0856 is present:
- The check engine light remains illuminated, indicating a persistent issue that needs attention.
- Erratic behavior of electronic features, such as power windows or door locks that fail to operate correctly, causing driver frustration.
- Poor engine performance characterized by hesitation during acceleration or stalling, which can affect driving safety.
- Intermittent warning lights on the dashboard, suggesting a lack of proper communication between modules.
- Decreased fuel efficiency, potentially by 10-15%, as the engine control module struggles to operate efficiently.
Possible Causes
Most common causes of U0856 (ordered by frequency):
- The most common cause of U0856 is a faulty Body Control Module (BCM), which accounts for about 40% of cases. This module can fail due to internal faults or software issues.
- Another frequent cause is damaged or corroded wiring and connectors, which can disrupt communication between modules. Inspect wiring harnesses for signs of wear or damage.
- A failing Powertrain Control Module (PCM) may also trigger this code, especially in older vehicles. Regular software updates and module checks can help prevent this.
- Less common but serious causes include issues with communication protocols, such as CAN bus failures, which can affect multiple systems in the vehicle.
- In rare cases, a complete module failure due to water intrusion or electrical surges can lead to this code being triggered.
U0856 Repair Costs
Cost Breakdown by Repair Type
BCM Replacement
Replacing the Body Control Module if it's found to be defective.
- Total: $300 - $800
- Success rate: 85%
Wiring Repair
Repairing or replacing damaged wiring or connectors linked to the BCM.
- Total: $150 - $300
- Success rate: 70%
PCM Reprogramming
Reprogramming the Powertrain Control Module to ensure correct communication.
- Total: $100 - $200
- Success rate: 80%
Money-Saving Tips for U0856
- 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 U0856 Diagnosis Process
Follow these systematic steps to accurately diagnose U0856. Each step builds on the previous one to ensure accurate diagnosis.
Step 1: Step 1: Conduct an initial visual inspection of wiring and connectors related to the BCM and other control modules for any signs of damage or corrosion (5-10 minutes)
Step 1: Conduct an initial visual inspection of wiring and connectors related to the BCM and other control modules for any signs of damage or corrosion (5-10 minutes).
Step 2: Step 2: Use the GeekOBD APP to perform an OBD2 scan, retrieving all codes and freeze frame data to analyze the context of the U0856 code (10-15 minutes)
Step 2: Use the GeekOBD APP to perform an OBD2 scan, retrieving all codes and freeze frame data to analyze the context of the U0856 code (10-15 minutes).
Step 3: Step 3: Test suspected components with a multimeter or OBD2 scanner to ensure they are functioning correctly (20-30 minutes)
Step 3: Test suspected components with a multimeter or OBD2 scanner to ensure they are functioning correctly (20-30 minutes).
Step 4: Step 4: After repairs, verify proper operation of the system and clear codes using the GeekOBD APP (10-15 minutes)
Step 4: After repairs, verify proper operation of the system and clear codes using the GeekOBD APP (10-15 minutes).
Step 5: Step 5: Conduct a road test under various driving conditions to confirm that the issue has been resolved and monitor for any reoccurrence of the code (15-20 minutes)
Step 5: Conduct a road test under various driving conditions to confirm that the issue has been resolved and monitor for any reoccurrence of the code (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 on 2016 Chevrolet Silverado 1500
Vehicle: 2016 Chevrolet Silverado 1500, 75,000 miles
Problem: Customer reported intermittent electrical issues and dashboard warning lights.
Diagnosis: After scanning with the GeekOBD APP, U0856 was detected. Visual inspection revealed corrosion on the BCM.
Solution: Replaced the BCM and reprogrammed it using the GeekOBD APP.
Cost: $500 including parts and labor.
Result: Post-repair, all electrical functions restored and no reoccurrence of U0856.
Case Study 2: Wiring Repair on 2017 GMC Sierra 1500
Vehicle: 2017 GMC Sierra 1500, 40,000 miles
Problem: Customer experienced power window failure and unstable dashboard readings.
Diagnosis: U0856 was present. Inspection revealed frayed wiring in the door harness.
Solution: Repaired the damaged wiring and ensured proper connections.
Cost: $200 for parts and labor.
Result: Electrical functions returned to normal and U0856 was cleared.