U0120moderate severityNetwork
Lost Communication with Starter/Generator Module
on 2021 Mazda Mazda3 2.5L I4 · FWD
What this code means
Cannot communicate with the integrated starter-generator in start-stop or mild hybrid vehicles.
Symptoms
- Start-stop system disabled
- Engine will not auto-restart
- Mild hybrid assist not available
- Warning message displayed
Common causes
- Starter-generator module failure
- CAN bus wiring
- Module power loss
- Belt-driven starter-generator fault
Diagnostic steps
- Check module fuse
- Test power and ground
- Check CAN wiring
- Test starter-generator operation
- Inspect drive belt condition
Repair notes
Check power supply and belt condition on belt-driven starter-generators.
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