U0009critical severityNetwork
High Speed CAN Communication Bus Shorted Together
on 2005 Mazda Mazda3 2.0L I4 · FWD
What this code means
CAN H and CAN L wires are shorted to each other, preventing differential signaling on the bus.
Symptoms
- Complete CAN bus failure
- No communication with any module on bus
- Vehicle may not start
Common causes
- CAN H and CAN L wires shorted together
- Connector pin damage
- Crushed wiring harness
- Rodent damage to wiring
Diagnostic steps
- Measure resistance between CAN H and CAN L (should be ~60 ohms with termination)
- Inspect wiring for physical damage
- Check connectors for bent pins
- Disconnect modules and measure resistance at each segment
Repair notes
Locate the short between CAN H and CAN L. Common in door jambs and under-dash wiring.
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
U0010
Medium Speed CAN Communication Bus
U0028
Vehicle Communication Bus A Performance