Lost Communication With Alternative Fuel Control Module
What it means
U0108 means the vehicle has lost communication with the alternative-fuel control module — the computer that manages a CNG, LPG, or bi-fuel system. When the engine controller can't talk to it, the alt-fuel system is usually disabled and the car falls back to gasoline, sometimes running poorly or refusing to start on alt fuel. The cause is normally a wiring, connector, power/ground, or bus fault at the module.
Can I keep driving? Often yes on gasoline — but the alternative-fuel system may be disabled and the engine can run poorly or refuse to start on alt fuel until it's fixed.
Common symptoms
What you'll notice
- Check-engine light and an alternative-fuel system warning on
- Alt-fuel (CNG/LPG) mode unavailable or vehicle reverts to gasoline
- Rough running, stalling, or no-start when on alternative fuel
- Scan tool cannot reach the alternative-fuel control module
Common causes
Most likely first
- Power or ground fault to the alternative-fuel control moduleLikely
- Damaged or corroded wiring/connector at the moduleCommon
- Failed alternative-fuel control moduleCommon
- CAN bus wiring fault between the module and the networkLess often
How to diagnose & fix
Work through it in order
- Confirm the code and check for other U-codes that point to a shared bus fault.
- Verify power and ground at the alternative-fuel control module.
- Inspect the module's wiring and connectors for damage or corrosion.
- Check CAN bus continuity to the module.
- Replace the module only after wiring, power, and ground check good; program if required.
FAQ
Quick answers
Is it safe to drive with U0108?+
Can I just clear U0108?+
Related codes
Often seen with U0108
Read & clear U0108 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.