U0038: CAN Bus B Performance Issue
The U0038 code indicates a performance problem on the Vehicle Communication Bus B, as defined by SAE J2012. This bus, typically a medium- or high-speed CAN bus depending on the vehicle architecture, is responsible for transmitting data between electronic modules. A 'performance' issue means that while communication is not completely interrupted, there are data integrity errors, excessive latency, or signal degradation that exceed the manufacturer's acceptable thresholds.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Abnormal resistance in the CAN B bus terminators
- High electrical resistance in bus B wiring due to oxidation or damage
- Poor contact or corrosion in bus B connectors
- Faulty CAN transceiver in a control module
- Electromagnetic interference on bus B wiring
- Impedance mismatch in the communication line
3. Symptoms You Will Notice
- Intermittent communication failures between modules
- Multiple related diagnostic trouble codes (DTCs) stored
4. Step-by-Step Diagnosis
Scan for all stored codes and freeze frame data
Inspect CAN B bus wiring and connectors for damage, corrosion, or loose connections
Measure resistance across the CAN B bus terminators (should be 60 ohms with two terminators)
Check for electromagnetic interference sources near the bus wiring
Test CAN transceiver operation in suspect modules using an oscilloscope
5. Frequently Asked Questions
Is it safe to drive?▼
The vehicle may still be drivable, but intermittent communication issues can cause unpredictable behavior. It is recommended to diagnose and repair the issue promptly to avoid potential safety concerns.
How much does it cost to fix?▼
Repair costs typically range from $100 to $500, depending on the root cause. Simple connector repairs may be under $100, while replacing a faulty module can exceed $500.