Quick Answer
U0120 means: U0120 indicates a loss of communication between vehicle control modules, often affecting performance and safety.
Can I drive with U0120? Immediate attention is recommended to prevent further damage or safety issues.
Common Questions
What does U0120 mean and how does it affect my car?
The U0120 code signifies a communication failure between critical vehicle control modules, impacting performance and safety. If ignored, it can lead to more severe issues like transmission failure.
What are the most common causes of U0120 and how much does it cost to fix?
Common causes include damaged wiring (40%), faulty control modules (30%), and poor ground connections. Repair costs can range from $100 to over $1,200 depending on the specific issue.
Can I drive my car with U0120 or should I stop immediately?
It's advisable to stop driving immediately as the vehicle may exhibit erratic behavior that can lead to safety risks. Ignoring the code can result in more extensive damage.
How can I diagnose U0120 myself using GeekOBD APP?
To diagnose U0120 with GeekOBD APP, first, connect the app to your vehicle's OBD2 port. Retrieve the DTCs and analyze any freeze frame data to identify patterns or additional codes that assist in diagnosing the issue.
What vehicles are most commonly affected by U0120?
Commonly affected vehicles include the 2015-2018 Chevrolet Silverado and GMC Sierra, among others with advanced electronic systems. Check for any recalls or Technical Service Bulletins (TSBs) related to this code.
How can I prevent U0120 from happening again?
Regular maintenance, including checking wiring and connectors for wear, ensuring proper grounding, and keeping software updated, can help prevent U0120 from recurring.
What is U0120?
The diagnostic trouble code (DTC) U0120 indicates a communication failure between the vehicle's control modules, specifically when the powertrain control module (PCM) cannot receive signals from another control module, such as the transmission control module (TCM) or body control module (BCM). This disruption can occur due to several reasons, including damaged wiring, faulty connectors, or issues with the control modules themselves. When U0120 is triggered, the vehicle may exhibit symptoms like warning lights on the dashboard, erratic engine behavior, or even limited functionality of certain systems. For instance, if the TCM is not communicating with the PCM, you may notice rough shifting or a complete failure of the transmission operation. This code is particularly common in vehicles like the 2015 Chevrolet Silverado and 2016 GMC Sierra, where electronic systems are heavily relied upon for optimal performance. Ignoring this code can lead to more severe issues over time, including potential failures of critical systems, which can compromise both safety and drivability.
System: U - Network (Communication, CAN Bus)
Symptoms
Common symptoms when U0120 is present:
- Check engine light stays on constantly, signaling an underlying issue that needs immediate attention.
- Engine hesitates during acceleration, making driving experience uncomfortable and potentially dangerous.
- Fuel economy decreases by 10-15%, which could lead to higher fuel costs over time.
- Transmission shifts are rough or erratic, indicating communication problems between the PCM and TCM.
- Dashboard warning lights for transmission or engine may illuminate, providing visual alerts of potential issues.
Possible Causes
Most common causes of U0120 (ordered by frequency):
- Most common cause: Damaged wiring or connectors, which accounts for about 40% of U0120 cases. This can occur due to wear and tear or rodent damage.
- Second most common cause: Faulty control module, typically the PCM or TCM, with a likelihood of around 30%. These modules can fail due to electrical issues or manufacturing defects.
- Third cause: Poor ground connections or corrosion on connectors, which can lead to intermittent communication failures. Regular inspections can help prevent this.
- Less common but serious cause: Software issues or bugs in the control modules, requiring a software update or reprogramming.
- Rare but possible cause: Faulty CAN bus wiring, which is necessary for communication between modules. This is a more complex issue that requires specialized diagnostic equipment.
U0120 Repair Costs
Cost Breakdown by Repair Type
Wiring Repair
Repair or replace damaged wiring and connectors that may cause communication failure.
- Total: $100 - $300
- Success rate: 85%
Control Module Replacement
Replace faulty PCM or TCM that is not communicating properly.
- Total: $400 - $1,200
- Success rate: 90%
Software Update
Perform a software update or reprogramming if the issue stems from software bugs.
- Total: $50 - $150
- Success rate: 75%
Money-Saving Tips for U0120
- 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 U0120 Diagnosis Process
Follow these systematic steps to accurately diagnose U0120. 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 the vehicle under various conditions to confirm repair success (15-20 minutes)
Step 5: Road test verification - Drive the 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: U0120 Communication Loss in 2016 Chevrolet Silverado
Vehicle: 2016 Chevrolet Silverado 1500, 50,000 miles
Problem: Customer reported check engine light and rough transmission shifts.
Diagnosis: Initial OBD2 scan revealed U0120. Visual inspection showed damaged wiring in the harness.
Solution: Repaired damaged wiring and cleared codes. Performed road test to confirm resolution.
Cost: $250 (including parts and labor)
Result: Transmission performance improved, and no further issues were reported.
Case Study 2: U0120 Error in 2015 GMC Sierra
Vehicle: 2015 GMC Sierra 2500HD, 75,000 miles
Problem: Engine hesitated during acceleration along with multiple dashboard warning lights.
Diagnosis: OBD2 scan revealed U0120. Found a faulty transmission control module.
Solution: Replaced the TCM and updated software. Conducted system tests to ensure proper function.
Cost: $900 (TCM replacement and labor)
Result: Vehicle performance restored, and the customer reported no further issues.