CAN network

U0108 — Lost Communication With Alternative Fuel Control Module

Severity: medium Drive with care, to a shop

What U0108 means

U0108 means another control module on the CAN bus stopped receiving messages from the alternative fuel (CNG or LPG) control module. That module normally manages the gas injectors, tank valves and switching between gasoline and gas. When it goes silent, the network flags a lost-communication fault.

Symptoms

  • Engine will not run on or switch to alternative fuel
  • Check Engine light on
  • Other warning lights may come on
  • Functions handled by the affected module are unavailable
  • Gas tank level not displayed

Possible causes

  1. Failed alternative fuel control module
  2. Open, shorted or chafed CAN bus wiring
  3. Corroded connectors or terminals
  4. Power or ground fault at the module (blown fuse, poor connection)
  5. Another faulty module loading down the bus
  6. Problems after an aftermarket gas system installation or modification
  7. Empty tank or the fuel system being switched off, so the module does not respond

How to diagnose

  1. Run a full-system scan to see which modules are not communicating
  2. Ask about any recent work on the gas system and confirm it is switched on
  3. Check the fuses and relays that feed the alternative fuel module
  4. Test power and ground at the module connector with a multimeter
  5. Inspect the harness and connectors for chafing, moisture and corrosion
  6. Measure CAN bus resistance and voltages at the diagnostic connector
  7. Unplug suspect modules one at a time only if the manufacturer procedure allows it
  8. Clear the code and see whether it returns

Common fixes

  • Restore power or ground to the module and replace any blown fuse
  • Repair or replace the damaged section of CAN wiring
  • Clean or replace corroded connectors and terminals
  • Replace or reprogram the alternative fuel control module
  • Replace another module that is loading the bus, if one is found

Questions and answers

What does U0108 mean?

It means communication with the alternative fuel (CNG/LPG) control module has been lost. Other modules are not receiving its messages over the CAN bus.

Can I drive with a U0108 code?

Usually yes, on gasoline, but gas mode may not work. If the engine runs rough or other warning lights appear, have it checked promptly.

How do I find the cause of U0108?

Start with the fuses, power and ground at the gas module, then inspect the wiring and connectors and test the CAN bus. If the wiring is fine, the module itself is the likely culprit.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.