What Does U0038 Mean?
Communication Bus B is functioning but with degraded performance, such as slow message transmission, intermittent communication, or excessive error frames. The network is operational but not meeting timing or quality specifications.
Common Causes
35%
High resistance in Bus B wiring or poor connector contacts
25%
Incorrect or degraded terminating resistor values on Bus B
20%
Electromagnetic interference from nearby components or aftermarket devices
15%
Module on Bus B experiencing internal failure or software corruption
5%
Low voltage or poor power supply to Bus B modules
Diagnostic Steps
1
Step 1: Use an oscilloscope to analyze Bus B signal quality, checking for proper voltage swings, rise/fall times, and noise
2
Step 2: Measure resistance between CAN-H and CAN-L at multiple points (should be consistent at 60-120 ohms)
3
Step 3: Check for voltage drops across connectors by measuring at multiple network access points
4
Step 4: Inspect wiring routing for proximity to high-current wires, motors, or ignition components that could cause EMI
5
Step 5: Monitor bus error counters using advanced scan tool to identify which module is generating errors
Estimated Repair Cost
$100 - $800
Parts + labor, varies by vehicle and location
Communication Bus B is functioning but with degraded performance, such as slow message transmission, intermittent communication, or excessive error frames. The network is operational but not meeting timing or quality specifications.
The most common cause of U0038 (Vehicle Communication Bus B Performance) is: High resistance in Bus B wiring or poor connector contacts
Typical repair costs for U0038 range from $100 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle remains drivable but may experience intermittent feature loss or erratic behavior of non-critical systems. Prolonged operation may lead to complete network failure.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0038 to identify the root cause.
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Quick Info
Category
Network
System
CAN Bus Network B Communication
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
