U0120 code meaning
Lost Communication With Starter/Generator Control Module
Network system Generic code U01xx codes Check engine light
What U0120 means
U0120 means the starter/generator control module, which drives an electric machine that can both crank the engine and produce electrical power, has dropped off the bus. Mitsubishi documents it for the Outlander PHEV (2018 and 2022): the hybrid controller (PHEV-ECU) sets U0120 when, after its supply has been within 10–16 V for more than 5 s, no frames from the generator control unit (GCU) housed within the power drive unit arrive for 0.3 s; confirmation uses the second of Mitsubishi’s OBD-II drive patterns, and whether the GCU itself has stored U0120 decides between replacing the GCU or the PHEV-ECU. Ford's 2014 powertrain code list also contains U0120. On 48 V mild hybrids with a belt or integrated starter generator it applies likewise. Expect lost start-stop or hybrid functions, a charging warning and the MIL.
U0120 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 5 hours
- Clears after repairAfter a drive cycle
Symptoms of U0120
- MIL and hybrid or charging warning
- Start-stop or engine start by the electric machine unavailable
- Battery not charged while driving
Common causes of U0120
- Most likelyFault on the CAN lines between hybrid controller and generator control unit
- PossibleStarter/generator control unit faulty (replacement if it stores U0120 itself)
- PossibleLow 12 V supply or poor ground at the power electronics
- Less likelyReceiving hybrid controller faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Starter generator moduleCAN bus wiring
What each part of U0120 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 20 | The exact fault in that area. |
What to do next
- Note U0120 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0120
What does U0120 mean?
U0120 means "Lost Communication With Starter/Generator Control Module". U0120 means the starter/generator control module, which drives an electric machine that can both crank the engine and produce electrical power, has dropped off the bus. It is a generic code, so it means the same on every make.
Is it safe to drive with U0120?
Drive gently and only to a workshop. With U0120 the car can go into limp mode (reduced power) to protect itself.
Will U0120 fail an emissions test?
Yes, it can. U0120 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U0120 to fix?
Difficulty: workshop only. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0120 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.