Quick Answer
U0939 means: DTC U0939 signifies a communication issue between vehicle control modules.
Can I drive with U0939? Immediate attention is recommended, as it may affect vehicle safety systems.
Common Questions
What does U0939 mean and how does it affect my car?
U0939 indicates a communication issue between electronic control modules in your vehicle. This can lead to malfunctioning systems, such as safety features and dashboard indicators, affecting your car's performance and safety.
What are the most common causes of U0939 and how much does it cost to fix?
Common causes include damaged wiring, faulty control modules, and software glitches. Repair costs can range from $100 for wiring repairs to $800 for module replacements, depending on the issue.
Can I drive my car with U0939 or should I stop immediately?
Driving with U0939 is not recommended, as it might affect critical safety systems. If you notice erratic behavior or warning lights, it's best to have it checked immediately.
How can I diagnose U0939 myself using GeekOBD APP?
Using the GeekOBD APP, you can perform an OBD2 scan to retrieve diagnostic trouble codes. Look for U0939 and any related codes to understand the context of the issue.
What vehicles are most commonly affected by U0939?
Commonly affected vehicles include the 2015-2020 Chevrolet Silverado and GMC Sierra, among others. Always check for any recalls related to electronic systems.
How can I prevent U0939 from happening again?
To prevent U0939, ensure regular inspections of wiring and connectors, avoid aftermarket modifications that might interfere with electronics, and keep your vehicle’s software updated.
What is U0939?
DTC U0939 indicates a communication error between control modules in your vehicle, specifically related to the Active Safety, Driver Assistance, or similar systems. This code typically arises when a control module, like the Body Control Module (BCM) or the Powertrain Control Module (PCM), cannot communicate effectively with another module. In vehicles such as the 2015-2020 Chevrolet Silverado and GMC Sierra, this can lead to issues such as malfunctioning safety features, erratic dashboard indicators, or even a complete failure of certain electronic systems. The implications can vary from minor annoyances, like warning lights on the dashboard, to significant safety concerns if critical functions, such as braking assistance or traction control, are affected. If you experience this code, it’s essential to address it promptly to ensure your vehicle operates as intended and to maintain safety on the road.
System: U - Network (Communication, CAN Bus)
Symptoms
Common symptoms when U0939 is present:
- Check engine light illuminates and remains on, indicating a persistent issue with vehicle electronics.
- Dashboard indicators for safety features, such as ABS or traction control, may flicker or remain on, signaling malfunction.
- Unexpected vehicle behavior, such as erratic braking or steering assistance, which can compromise safety.
- Inconsistent performance in driver assistance features, like lane departure warnings or adaptive cruise control.
- Poor fuel economy due to malfunctioning engine management systems affected by the communication error.
Possible Causes
Most common causes of U0939 (ordered by frequency):
- The most common cause of U0939 is damaged or corroded wiring connecting the control modules, with a likelihood of about 60%. Regular inspections can help prevent this.
- Another potential cause is a faulty control module itself, which may fail to communicate due to internal issues. This has a likelihood of 25%. Replacement is often the only solution.
- Interference from aftermarket modifications, such as non-OEM parts or improper installations, can cause communication issues, with about a 10% likelihood. Always use high-quality parts.
- Less commonly, software glitches within the vehicle's computer system can lead to U0939. This is rare but may require a software update or reprogramming to resolve.
- In very rare cases, a low battery voltage can cause communication errors, affecting multiple modules. Regular battery maintenance can help avoid this situation.
U0939 Repair Costs
Cost Breakdown by Repair Type
Wiring Repair
Repair or replace damaged wiring harness.
- Total: $100 - $300
- Success rate: 85%
Control Module Replacement
Replace faulty control module with OEM part.
- Total: $300 - $800
- Success rate: 90%
Software Update
Reprogram or update vehicle's software.
- Total: $50 - $150
- Success rate: 75%
Money-Saving Tips for U0939
- 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 U0939 Diagnosis Process
Follow these systematic steps to accurately diagnose U0939. 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 (5-10 minutes)
Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion (5-10 minutes).
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes)
Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes).
Step 3: Step 3: Component testing - Use a multimeter or specific diagnostic tools to test suspected components (20-30 minutes)
Step 3: Component testing - Use a multimeter or specific diagnostic tools to test suspected components (20-30 minutes).
Step 4: Step 4: System function test - Verify proper operation after repairs and clear codes (10-15 minutes)
Step 4: System function test - Verify proper operation after repairs and clear codes (10-15 minutes).
Step 5: Step 5: Road test verification - Drive vehicle under various conditions to confirm repair success (15-20 minutes)
Step 5: Road test verification - Drive vehicle under various conditions to confirm repair success (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: Wiring Repair on 2017 Chevrolet Silverado
Vehicle: 2017 Chevrolet Silverado, 53,000 miles
Problem: Customer reported intermittent ABS light and traction control issues.
Diagnosis: Visual inspection revealed corroded wiring harness connecting to the ABS module.
Solution: Replaced the damaged wiring and reconnected terminals.
Cost: $250 for parts and labor
Result: ABS and traction control systems functioned normally after repair.
Case Study 2: Control Module Replacement in 2018 GMC Sierra
Vehicle: 2018 GMC Sierra, 40,000 miles
Problem: Customer experienced dashboard warning lights and failed driver assistance features.
Diagnosis: OBD2 scan revealed U0939 and a fault in the Body Control Module.
Solution: Replaced the Body Control Module with an OEM part and reprogrammed it.
Cost: $600 for parts and labor
Result: All systems returned to normal operation after the fix.