Quick Answer
U0391 means: U0391 signifies a communication error between vehicle control modules.
Can I drive with U0391? Address immediately to avoid further electrical issues.
Common Questions
What does U0391 mean and how does it affect my car?
U0391 signifies a communication issue between your vehicle's control modules, which can lead to performance problems like stalling or poor acceleration. It's essential to resolve this code to ensure your vehicle operates safely and efficiently.
What are the most common causes of U0391 and how much does it cost to fix?
The most common causes of U0391 include faulty control modules (60%), damaged wiring (25%), and connector corrosion. Repair costs can range from $100 for wiring repairs to $1200 for control module replacements.
Can I drive my car with U0391 or should I stop immediately?
It's advisable to stop driving your vehicle if you see the U0391 code, as it can cause erratic behavior and possibly lead to unsafe driving conditions. Addressing the issue promptly is crucial.
How can I diagnose U0391 myself using GeekOBD APP?
Using the GeekOBD APP, you can connect to your vehicle's OBD2 port to retrieve the U0391 code. Make sure to check freeze frame data for context and take note of any other codes that might be present.
What vehicles are most commonly affected by U0391?
U0391 is frequently reported in vehicles like the 2015-2020 Ford F-150 and similar models that rely on multiple electronic control modules. Check for any recalls or technical service bulletins related to your vehicle.
How can I prevent U0391 from happening again?
Regular maintenance checks, including inspecting wiring and connections for corrosion, can help prevent the recurrence of U0391. Keeping your vehicle's software updated is also essential.
What is U0391?
DTC U0391 indicates a communication error between the vehicle's control modules, specifically signaling that a module is not responding as expected. This code often arises in modern vehicles that rely heavily on interconnected systems for proper operation. When the onboard diagnostics system detects that a particular control module, such as the transmission control module or the body control module, fails to communicate with the engine control unit (ECU) or other modules, it generates this code. The implications of this code can vary widely, ranging from minor inconveniences, like the inability to use certain features, to significant safety issues if critical systems are affected. Vehicle owners may notice symptoms such as warning lights on the dashboard, erratic behavior of electronic components, or even performance issues like stalling or rough idling. It's important to address this code promptly as unresolved communication issues can lead to further electrical problems and potentially unsafe driving conditions.
System: U - Network (Communication, CAN Bus)
Symptoms
Common symptoms when U0391 is present:
- Check engine light stays on constantly, indicating a persistent fault that needs attention.
- Dashboard warning lights are erratic, with multiple alerts appearing simultaneously, confusing the driver.
- Performance issues, such as the vehicle stalling or experiencing rough idling, particularly when starting.
- Inability to use certain electronic features, such as power windows or the radio, due to communication failures.
- Decreased fuel economy as the engine struggles to operate efficiently without proper module communication.
Possible Causes
Most common causes of U0391 (ordered by frequency):
- The most common cause is a faulty control module, which occurs in about 60% of cases, often due to wear or electrical failure.
- Another frequent issue is damaged wiring or connectors, which can disrupt communication between modules, making up about 25% of U0391 occurrences.
- Corrosion or poor connections at the module terminals can lead to intermittent communication problems; regular inspection can prevent this.
- Less common but serious causes include software issues within the control module that may require reprogramming or updates.
- A rare cause could be a short circuit in the wiring harness, which can lead to significant electrical issues if not addressed promptly.
U0391 Repair Costs
Cost Breakdown by Repair Type
Control Module Replacement
Replacing a faulty control module, which is often the root cause of U0391.
- Total: $400 - $1200
- Success rate: 85%
Wiring Repair
Repairing damaged wiring or connectors that disrupt communication.
- Total: $100 - $500
- Success rate: 90%
Money-Saving Tips for U0391
- 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 U0391 Diagnosis Process
Follow these systematic steps to accurately diagnose U0391. 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, which takes about 5-10 minutes
Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion, which takes about 5-10 minutes.
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context, requiring around 10-15 minutes
Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context, requiring around 10-15 minutes.
Step 3: Step 3: Component testing - Use a multimeter or specific diagnostic tools to test suspected components, which may take 20-30 minutes
Step 3: Component testing - Use a multimeter or specific diagnostic tools to test suspected components, which may take 20-30 minutes.
Step 4: Step 4: System function test - Verify proper operation after repairs and clear codes; this step should take about 10-15 minutes
Step 4: System function test - Verify proper operation after repairs and clear codes; this step should take about 10-15 minutes.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success, which will take approximately 15-20 minutes
Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success, which will take approximately 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: Ford F-150 U0391 Repair Case Study
Vehicle: 2018 Ford F-150, 45,000 miles
Problem: Customer reported engine stalling and dashboard warning lights.
Diagnosis: After scanning with the GeekOBD APP, U0391 was confirmed along with a faulty body control module.
Solution: Replaced the body control module and repaired some damaged wiring.
Cost: $800 (including parts and labor)
Result: Vehicle performance improved significantly with all features functioning properly.
Case Study 2: Chevy Silverado Communication Issue
Vehicle: 2017 Chevrolet Silverado 1500, 60,000 miles
Problem: Customer experienced erratic electrical behavior and check engine light.
Diagnosis: Diagnostic steps revealed U0391 due to corroded connectors.
Solution: Cleaned corroded connectors and secured all wiring.
Cost: $150 (for labor and cleaning materials)
Result: Resolved the issue, and the vehicle operated normally after the repair.