High Speed CAN Communication Bus (+) Open
2011-2011 Subaru Legacy 2.5L H4
The 2011 Subaru Legacy is equipped with a 2.5L flat-4 engine. Below you'll find detailed u0003 diagnostic code information including labor time estimates, cost ranges, and technician notes specific to this engine configuration.
Description
The CAN High wire is open, disrupting high-speed bus communication. CAN H carries the dominant high signal.
Symptoms
- Multiple modules offline
- Warning lights illuminated
- Systems inoperative
- No scan tool communication on some modules
Common Causes
- Broken CAN H wire
- Corroded CAN H terminal
- Damaged CAN bus connector
- Wiring harness damage
Diagnostic Steps
- Measure voltage on CAN H (should be ~2.5V idle, ~3.5V dominant)
- Check continuity of CAN H wire
- Inspect CAN bus connectors
- Locate break using voltage drop test
Repair Notes
Locate and repair the open in the CAN H wire. Check all splice points.
Related Codes
Other Network Codes
- U0001High Speed CAN Communication Bus
- U0002High Speed CAN Communication Bus Performance
- U0004High Speed CAN Communication Bus (+) Low
- U0005High Speed CAN Communication Bus (+) High
- U0006High Speed CAN Communication Bus (-) Open
- U0007High Speed CAN Communication Bus (-) Low
- U0008High Speed CAN Communication Bus (-) High
- U0009High Speed CAN Communication Bus Shorted Together
- U0010Medium Speed CAN Communication Bus
- U0028Vehicle Communication Bus A Performance
U0003 on Other Vehicles
Common Questions
What does code U0003 mean on a 2011-2011 Subaru Legacy?
U0003 stands for "High Speed CAN Communication Bus (+) Open". The CAN High wire is open, disrupting high-speed bus communication. CAN H carries the dominant high signal.
What are the symptoms of U0003 on a Subaru Legacy?
Common symptoms of U0003 include: Multiple modules offline, Warning lights illuminated, Systems inoperative, No scan tool communication on some modules.
What causes U0003 on a 2011-2011 Subaru Legacy?
Common causes of U0003 include: Broken CAN H wire, Corroded CAN H terminal, Damaged CAN bus connector, Wiring harness damage.
Last updated: March 2026