What Does U0018 Mean?
The CAN Low and CAN High wires on the medium-speed network are shorted together, eliminating the differential voltage needed for communication. This completely disables network functionality.
Safety Warning
Complete loss of medium-speed network communication disables multiple vehicle systems. Vehicle may not start, shift properly, or operate safety systems, making it unsafe to drive.
Common Causes
40%
Wire insulation breakdown causing direct contact between CAN High and CAN Low
25%
Connector pin-to-pin short due to corrosion or foreign material
20%
Failed control module with internal short between CAN circuits
10%
Crushed or severely damaged harness from collision or pinch point
5%
Improper repair with wires crossed or incorrectly spliced
Diagnostic Steps
1
Step 1: Measure resistance between CAN High and CAN Low circuits with modules disconnected (should be approximately 60 ohms from termination resistors only)
2
Step 2: If resistance is near zero ohms, disconnect connectors progressively to isolate the short location
3
Step 3: Inspect all connectors for pushed-out pins, corrosion bridges, or contamination between adjacent terminals
4
Step 4: Examine harness for crush damage, especially at routing points near moving components or sharp edges
5
Step 5: Test individual modules on bench if harness checks good to identify internal module fault
Estimated Repair Cost
$200 - $2,500
Parts + labor, varies by vehicle and location
The CAN Low and CAN High wires on the medium-speed network are shorted together, eliminating the differential voltage needed for communication. This completely disables network functionality.
The most common cause of U0018 (Medium Speed CAN Communication Bus (-) shorted to Bus (+)) is: Wire insulation breakdown causing direct contact between CAN High and CAN Low
Typical repair costs for U0018 range from $200 to $2,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Complete loss of medium-speed network communication disables multiple vehicle systems. Vehicle may not start, shift properly, or operate safety systems, making it unsafe to drive.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0018 to identify the root cause.
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Quick Info
Category
Network
System
Network Communication System
Difficulty
Type
Generic (SAE)
Recommended Tools
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