U055A: Special Purpose A Module Invalid Data
Diagnostic trouble code U055A indicates that the powertrain control module (PCM) or a central network module has received invalid or erroneous data from the 'Special Purpose A' control module. This is a network communication code (U-class) per SAE J2012, which standardizes module-to-module communication over the Controller Area Network (CAN) bus. 'Special purpose' typically refers to an auxiliary or accessory module that is not part of the main drivetrain but still needs to exchange data on the vehicle network. The data invalidity is detected through checksum verification, error counting, or frame synchronization failures.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Internal failure of the Special Purpose A control module
- Open or short circuit in the CAN bus wiring
- Loose, corroded, or poorly grounded connections in the module harness
- Loss of power or ground supply to the transmitting module
- Electromagnetic interference (EMI) affecting the CAN bus signal
- Fault in the receiving module (PCM or gateway) that interprets the data
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Malfunction of systems controlled by the Special Purpose A module (e.g., auxiliary lighting, accessories)
4. Step-by-Step Diagnosis
Scan for all stored codes and freeze frame data
Inspect the CAN bus wiring and connectors for damage, corrosion, or loose pins
Check power and ground circuits at the Special Purpose A module
Test the module's internal operation using a scan tool or oscilloscope
Verify communication with other modules on the network
5. Frequently Asked Questions
Is it safe to drive?▼
The vehicle may still be drivable, but the affected module's functions may be impaired. It is recommended to diagnose and repair the issue promptly to avoid further electrical problems.
How much does it cost to fix?▼
Repair costs vary widely depending on the root cause. A simple wiring repair may cost $100-$200, while replacing a module can range from $300 to $800 or more, including labor.