OBD-II code · Network
U0120 Lost Communication with Starter/Generator Control Module
The Starter/Generator Control Module has stopped transmitting on the vehicle data bus, so other control units no longer receive its messages. Stop-start and mild-hybrid generator functions stop working. Typical causes are loss of power or ground at the module, an open or shorted CAN/LIN bus wire, a connector fault, or an internal module failure.
Is it safe to drive with U0120?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyStarter/generator module unpowered
- PossibleCAN wiring to starter/generator broken
- Less likelyGateway module routing CAN messages incorrectly
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1.5–6 h
- Emissions test
- Likely to fail
- Parts involved
- Starter Generator Module, Can Bus Wiring
Related codes
- U011DLost Communication With All Wheel Drive Control Module
- U011ELost Communication With Throttle Actuator B Control Module
- U011FLost Communication With V2X Module
- U0121Lost Communication with ABS Control Module
- U0122Lost Communication with Vehicle Dynamics Control Module
- U0123Lost Communication with Yaw Rate Sensor Module
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.