What Does U0043 Mean?
The negative wire of communication bus B is shorted to ground or has voltage below specification. This disrupts network communication between modules on this bus circuit.
Common Causes
40%
CAN bus B(-) wire damaged, chafed, or shorted to ground
30%
Faulty control module pulling bus line low
20%
Corroded or damaged connector terminals on bus B circuit
10%
Water intrusion causing short to ground in harness
Diagnostic Steps
1
Step 1: Visually inspect all connectors and wiring on bus B circuit for damage, corrosion, or water intrusion
2
Step 2: Measure voltage on CAN B(-) line at multiple points; should read approximately 2.5V when bus is idle
3
Step 3: Check resistance between CAN B(-) and ground; should show infinite resistance (open circuit)
4
Step 4: Disconnect modules one at a time to isolate faulty module pulling bus low
5
Step 5: Repair or replace damaged wiring, connectors, or faulty module as identified
Estimated Repair Cost
$150 - $1,200
Parts + labor, varies by vehicle and location
The negative wire of communication bus B is shorted to ground or has voltage below specification. This disrupts network communication between modules on this bus circuit.
The most common cause of U0043 (Vehicle Communication Bus B (-) Low) is: CAN bus B(-) wire damaged, chafed, or shorted to ground
Typical repair costs for U0043 range from $150 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
May cause loss of critical vehicle functions including engine performance, transmission operation, or safety systems. Vehicle may enter limp mode or fail to start.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0043 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Network
System
Vehicle Communication Network
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
