Quick Answer
U0991 means: DTC U0991 indicates a communication error between vehicle modules.
Can I drive with U0991? Immediate attention is recommended to avoid further complications.
Common Questions
What does U0991 mean and how does it affect my car?
DTC U0991 signifies a communication error between the vehicle's control modules. This can lead to various performance issues, such as erratic shifting, stalling, or even failure to start. It's critical to address this to maintain your vehicle's reliability.
What are the most common causes of U0991 and how much does it cost to fix?
Common causes of U0991 include damaged wiring (40% likelihood), malfunctioning control modules, and poor grounding. Repair costs can range from $100 to $1,200, depending on the specific issue.
Can I drive my car with U0991 or should I stop immediately?
It's advisable to stop driving immediately if you see the U0991 code. Continuing to drive could lead to further damage and more expensive repairs.
How can I diagnose U0991 myself using GeekOBD APP?
To diagnose U0991 with the GeekOBD APP, connect it to your vehicle’s OBD2 port, retrieve the trouble codes, and analyze the freeze-frame data. Pay attention to any related codes that might give clues to the underlying issue.
What vehicles are most commonly affected by U0991?
DTC U0991 is commonly found in 2011-2017 Ford F-150 models, as well as other Ford vehicles from that period. It's essential to stay updated on any recalls that may relate to communication failures in your specific model.
How can I prevent U0991 from happening again?
Regular maintenance, including inspecting wiring and connectors, ensuring good grounds, and keeping electrical components clean and dry, can help prevent U0991 from recurring.
What is U0991?
The DTC U0991 code indicates a communication error between the vehicle's modules, specifically relating to the inability to communicate with a specific control module. This trouble code often surfaces in vehicles such as the 2011-2017 Ford F-150, among others. When your car's onboard diagnostics (OBD2) system detects a disruption in communication, it triggers this code, indicating that there’s a problem in the network of modules responsible for various vehicle functions. For instance, it could mean that your powertrain control module (PCM) isn't getting the necessary information from the transmission control module (TCM) or another essential component. The practical implication of this code is that it can affect numerous vehicle systems, leading to issues such as erratic shifting, failure to start, or even complete engine shutdown in severe cases. Ignoring this code can lead to increased repair costs and may compromise your vehicle's safety. Therefore, understanding and addressing DTC U0991 promptly is crucial for maintaining the performance and reliability of your car.
System: U - Network (Communication, CAN Bus)
Symptoms
Common symptoms when U0991 is present:
- Check engine light remains illuminated, indicating a general fault in the vehicle's communication system.
- Erratic shifting patterns, where the transmission may hesitate or shift harshly during driving.
- Engine performance issues, such as rough idling or stalling while driving, which can be linked to communication failures.
- Inability to start the engine, which may be caused by the PCM not receiving vital signals from other control modules.
- Decreased fuel economy, potentially leading to a drop in mileage of 5-15% due to improper engine management.
Possible Causes
Most common causes of U0991 (ordered by frequency):
- The most common cause of DTC U0991 is damaged wiring or connectors, which account for about 40% of cases. Corrosion or loose connections can disrupt communication between modules.
- Another frequent cause is a malfunctioning control module, such as the PCM or TCM, due to software glitches or hardware failures that prevent proper signaling.
- Poor grounding in the vehicle's electrical system can lead to intermittent communication issues, making it crucial to regularly inspect grounding points.
- Less common but serious causes include water intrusion into control modules, which can cause significant damage and require module replacement.
- In rare cases, aftermarket modifications or accessories may interfere with the vehicle's network, leading to communication errors.
U0991 Repair Costs
Cost Breakdown by Repair Type
Wiring Repair
Repair of damaged wiring or connectors to restore communication.
- Total: $150 - $300
- Success rate: 85%
Control Module Replacement
Replacing a faulty control module with a new or refurbished unit.
- Total: $500 - $1,200
- Success rate: 90%
Grounding Repair
Correcting grounding issues or corrosion to ensure proper electrical flow.
- Total: $100 - $200
- Success rate: 75%
Money-Saving Tips for U0991
- 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 U0991 Diagnosis Process
Follow these systematic steps to accurately diagnose U0991. Each step builds on the previous one to ensure accurate diagnosis.
Step 1: Step 1: Initial visual inspection - Check for any visible damage to wiring, connectors, or signs of corrosion (5-10 minutes)
Step 1: Initial visual inspection - Check for any visible damage to wiring, connectors, or signs of corrosion (5-10 minutes).
Step 2: Step 2: OBD2 scan with GeekOBD APP - Use the GeekOBD APP to retrieve all codes and freeze-frame data, helping to establish the context of the fault (10-15 minutes)
Step 2: OBD2 scan with GeekOBD APP - Use the GeekOBD APP to retrieve all codes and freeze-frame data, helping to establish the context of the fault (10-15 minutes).
Step 3: Step 3: Component testing - Employ a multimeter or an oscilloscope to test the suspected components for proper functionality (20-30 minutes)
Step 3: Component testing - Employ a multimeter or an oscilloscope to test the suspected components for proper functionality (20-30 minutes).
Step 4: Step 4: System function test - After performing repairs, verify that all modules are communicating correctly and clear any stored codes (10-15 minutes)
Step 4: System function test - After performing repairs, verify that all modules are communicating correctly and clear any stored codes (10-15 minutes).
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to ensure that the problem has been resolved (15-20 minutes)
Step 5: Road test verification - Drive the vehicle under various conditions to ensure that the problem has been resolved (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 2015 Ford F-150
Vehicle: 2015 Ford F-150, 75,000 miles
Problem: Customer reported check engine light and erratic shifting.
Diagnosis: After scanning with GeekOBD APP, U0991 was the primary code. Visual inspection revealed damaged wiring in the harness.
Solution: Repaired the damaged wiring and secured loose connectors.
Cost: $250
Result: The vehicle shifted smoothly after repairs, and the check engine light was cleared successfully.
Case Study 2: Control Module Replacement for 2013 Ford Explorer
Vehicle: 2013 Ford Explorer, 90,000 miles
Problem: Customer experienced stalling and failure to start.
Diagnosis: DTC U0991 was triggered due to a failing PCM identified through diagnostic testing.
Solution: Replaced the faulty PCM with a new unit, reprogrammed it, and cleared the codes.
Cost: $950
Result: The Explorer started without issues, and the performance was restored.