What Does U0042 Mean?
The negative signal wire (CAN-L) of Communication Bus B has an open circuit, breaking the differential signal pair needed for network communication. This prevents proper data transmission on Bus B.
Common Causes
40%
Broken or cut CAN-L wire in Bus B harness
30%
Disconnected or loose connector on Bus B network
20%
Corroded or damaged terminal causing open in CAN-L line
10%
Failed module with internal open on CAN-L circuit
Diagnostic Steps
1
Step 1: Verify open circuit by measuring continuity on CAN-L wire throughout Bus B network
2
Step 2: Backprobe connectors at various modules to narrow down which harness section has the open
3
Step 3: Inspect all Bus B connectors for pushed-back pins, terminal corrosion, or poor terminal retention
4
Step 4: Check wiring at flex points such as door jambs, under seats, or trunk hinges for broken conductors
5
Step 5: Repair broken wire or replace damaged connector, ensuring proper crimping and sealing
Estimated Repair Cost
$150 - $900
Parts + labor, varies by vehicle and location
The negative signal wire (CAN-L) of Communication Bus B has an open circuit, breaking the differential signal pair needed for network communication. This prevents proper data transmission on Bus B.
The most common cause of U0042 (Vehicle Communication Bus B (-) Open) is: Broken or cut CAN-L wire in Bus B harness
Typical repair costs for U0042 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 become inoperative. Vehicle remains drivable but may display multiple warning lights and lose 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 U0042 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.
