OBD2 Code U0099: Reserved CAN Bus Fault
Diagnostic trouble code U0099 is a reserved code under the SAE J2012 standard, meaning it does not have a publicly assigned definition. It falls within the range of codes (U0000-U0099) designated for communication faults on the Controller Area Network (CAN) bus. This code is typically manufacturer-specific or proprietary, requiring OEM documentation for accurate diagnosis. It may indicate a communication failure in a network module not covered by public standards, a software glitch, or data bus interference.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Manufacturer-specific or proprietary code requiring OEM documentation
- Possible communication failure in a network module not defined in public standards
- Control module programming or software update error
- Interference on the vehicle's communication data bus
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Intermittent or complete loss of communication with certain modules
4. Step-by-Step Diagnosis
Use a professional scan tool to retrieve all stored codes and freeze frame data
Consult OEM service information for the specific vehicle make and model
Inspect CAN bus wiring and connectors for damage, corrosion, or loose connections
Check for any recent software updates or programming changes that may have caused the fault
5. Frequently Asked Questions
Is it safe to drive?▼
The severity is medium. While the vehicle may still be drivable, the underlying communication issue could affect critical systems. It is recommended to have it diagnosed promptly to avoid potential safety risks.
How much does it cost to fix?▼
Diagnosis typically costs $100-$200. Repair costs vary widely depending on the root cause, ranging from $50 for a loose connection to $1,000+ for module replacement or reprogramming.