What Does U0012 Mean?
The CAN High (positive) wire on the medium-speed network has an open circuit or break, preventing proper differential signaling. One half of the twisted pair is not conducting, causing communication failure.
Common Causes
35%
Broken or cut CAN High wire in harness, often at flex points or areas subject to abrasion
30%
Corroded connector terminal or pushed-out pin on CAN High circuit preventing continuity
15%
Failed splice or repair in CAN High wire creating open circuit
12%
Module connector terminal damaged or not fully seated, breaking CAN High connection
8%
Rodent damage or environmental degradation causing open in CAN High wire
Diagnostic Steps
1
Step 1: Verify open circuit by measuring continuity on CAN High wire from end-to-end with all modules disconnected (should have continuous path)
2
Step 2: Systematically disconnect intermediate connectors along CAN High circuit while checking continuity to isolate the section containing the break
3
Step 3: Carefully inspect identified harness section for visible damage, cuts, or areas where wire may be pinched or abraded
4
Step 4: Check all connector terminals for proper seating, corrosion, or terminal push-back using terminal test kit
5
Step 5: If open is within a sealed harness section, use time-domain reflectometry (TDR) or capacitance testing to pinpoint exact location of break
Estimated Repair Cost
$150 - $1,200
Parts + labor, varies by vehicle and location
The CAN High (positive) wire on the medium-speed network has an open circuit or break, preventing proper differential signaling. One half of the twisted pair is not conducting, causing communication failure.
The most common cause of U0012 (Medium Speed CAN Communication Bus (+) Open) is: Broken or cut CAN High wire in harness, often at flex points or areas subject to abrasion
Typical repair costs for U0012 range from $150 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Medium-speed network failure typically affects comfort and convenience systems rather than critical safety functions. Vehicle remains safe to drive but may have inoperative features and warning lights.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0012 to identify the root cause.
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Quick Info
Category
Network
System
Network Communications
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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