What Does U0003 Mean?
The CAN High (+) circuit has an open condition, meaning there is a break or disconnection in the positive wire of the twisted pair communication bus. Communication on the network will be severely compromised or non-existent.
Safety Warning
Vehicle will likely not start or will have multiple system failures including safety-critical systems. Do not drive until repaired.
Common Causes
40%
Broken or severed CAN High wire in harness
30%
Disconnected or damaged connector on CAN High circuit
15%
Failed control module with open CAN High pin
10%
Corroded terminal causing complete circuit interruption
5%
Damage from previous repair or collision
Diagnostic Steps
1
Step 1: Measure voltage on CAN High circuit at multiple points; should read approximately 2.5-3.5V with key on if circuit is intact
2
Step 2: Perform continuity test on CAN High wire from end to end with key off and appropriate modules disconnected
3
Step 3: Visually inspect CAN High wire routing for signs of damage, cuts, or pinch points
4
Step 4: Check all connectors in CAN High circuit for pushed-out pins, corrosion, or damage
5
Step 5: Use wiring diagram to trace CAN High circuit and isolate the open section by testing at junction points
Estimated Repair Cost
$150 - $1,200
Parts + labor, varies by vehicle and location
The CAN High (+) circuit has an open condition, meaning there is a break or disconnection in the positive wire of the twisted pair communication bus. Communication on the network will be severely compromised or non-existent.
The most common cause of U0003 (High Speed CAN Communication Bus (+) Open) is: Broken or severed CAN High wire in harness
Typical repair costs for U0003 range from $150 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle will likely not start or will have multiple system failures including safety-critical systems. Do not drive until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0003 to identify the root cause.
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Quick Info
Category
Network
System
Network Communication
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
