What Does U0039 Mean?
The positive signal wire (CAN-H) of Communication Bus B has an open circuit, preventing proper signal transmission. This breaks the differential signal pair required for network communication.
Common Causes
40%
Broken or cut CAN-H wire in Bus B harness
30%
Disconnected or loose connector on Bus B network
20%
Corroded terminal causing open circuit in CAN-H line
10%
Failed module with internal open on CAN-H output
Diagnostic Steps
1
Step 1: Verify open circuit by measuring continuity on CAN-H wire throughout Bus B network
2
Step 2: Backprobe connectors at multiple modules to isolate which harness section contains the open
3
Step 3: Inspect connectors for pushed-out pins, corrosion, or damaged terminal retention
4
Step 4: Check for obvious wire damage, especially at flex points near doors, seats, or trunk
5
Step 5: Repair broken wire or replace damaged connector, ensuring proper terminal seating and strain relief
Estimated Repair Cost
$150 - $900
Parts + labor, varies by vehicle and location
The positive signal wire (CAN-H) of Communication Bus B has an open circuit, preventing proper signal transmission. This breaks the differential signal pair required for network communication.
The most common cause of U0039 (Vehicle Communication Bus B (+) Open) is: Broken or cut CAN-H wire in Bus B harness
Typical repair costs for U0039 range from $150 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Non-critical systems on Bus B will be inoperative. Vehicle typically remains drivable but may have warnings and reduced functionality for comfort or convenience features.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0039 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.
