Network, generic

U0108 Lost Communication With Alternative Fuel Control Module

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Alternative fuel module without power or ground (fuse, relay)
Damaged CAN wiring between conversion module and PCM
Water or corrosion in the module connectors
Alternative fuel module internally faulty

Symptoms

  • MIL on
  • Rough idle or poor running on the alternative fuel
  • System may stay on or revert to gasoline

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–800
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

alt fuel modulecan bus wiring

Related codes

U0309U0409U0100

References: roushcleantech.com, law.cornell.edu.