U1040moderate severityNetwork
Lost Communication - General Bus Timeout
on 2004 Subaru Legacy 3.0L H6 · AWD
What this code means
General timeout on the communication bus. Multiple modules are not responding within expected time.
Symptoms
- Multiple systems intermittently offline
- General communication degradation
- Multiple timeout DTCs stored
- Scan tool slow response
Common causes
- CAN bus overloaded
- Poor bus termination
- Multiple modules with slow response
- Bus wiring degradation
- Power supply instability affecting modules
Diagnostic steps
- Check bus termination resistance
- Monitor bus load with scope
- Check power supply voltage to modules
- Test for intermittent connections
- Remove aftermarket CAN devices
Repair notes
Check bus termination and overall bus health. Overloaded buses cause timeouts.
Other Network codes on this vehicle
U0001
High Speed CAN Communication Bus
U0002
High Speed CAN Communication Bus Performance
U0003
High Speed CAN Communication Bus (+) Open
U0004
High Speed CAN Communication Bus (+) Low
U0005
High Speed CAN Communication Bus (+) High
U0006
High Speed CAN Communication Bus (-) Open
U0007
High Speed CAN Communication Bus (-) Low
U0008
High Speed CAN Communication Bus (-) High
U0009
High Speed CAN Communication Bus Shorted Together
U0010
Medium Speed CAN Communication Bus