U0108 code meaning
Lost Communication With Alternative Fuel Control Module
Network system Generic code U01xx codes Check engine light
What U0108 means
U0108 covers a separate controller for an alternative fuel such as LPG or CNG, added to an engine that otherwise runs a gasoline control strategy. Roush CleanTech's fourth-generation propane systems for Ford E- and F-Series trucks (2016–2018) are a documented user: the PCM expects CAN traffic from the system's Smart Relay Module and stores U0108 when those messages keep missing. Roush lists broken wiring between SRM and PCM, a blown fuse and lost power or ground at the SRM as causes, rough idle as a symptom. Under CARB rules, every electronic powertrain part that can raise emissions falls under comprehensive component monitoring, which makes the link emission-relevant. U0409 covers implausible data, U0309 a software mismatch.
U0108 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0108
- MIL on
- Rough idle or poor running on the alternative fuel
- System may stay on or revert to gasoline
Common causes of U0108
- Most likelyAlternative fuel module without power or ground (fuse, relay)
- PossibleDamaged CAN wiring between conversion module and PCM
- PossibleWater or corrosion in the module connectors
- Less likelyAlternative fuel module internally faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Alt fuel moduleCAN bus wiring
What each part of U0108 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 08 | The exact fault in that area. |
What to do next
- Note U0108 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 U0108
What does U0108 mean?
U0108 means "Lost Communication With Alternative Fuel Control Module". U0108 covers a separate controller for an alternative fuel such as LPG or CNG, added to an engine that otherwise runs a gasoline control strategy. It is a generic code, so it means the same on every make.
Is it safe to drive with U0108?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U0108 fail an emissions test?
Yes, it can. U0108 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 U0108 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U0108 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.