U0108

Lost Communication With Alternative Fuel Control Module

Communication network / alternative fuel Generic OBD-II Medium

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.

Medium

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.

Real-world scan data

Seen in

660

scans in the past year

Found in

0.1%

of scans

0.2%

of scans that found faults

Appears alongside · share of U0108 scans

U0100in 17.6% of scans

U0155in 11.4% of scans

U0073in 10.8% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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?+

On a bi-fuel vehicle you can usually run on gasoline, but the alt-fuel system may be offline and could stall or fail to start on gas. Have it diagnosed before depending on alt fuel.

Can I just clear U0108?+

It returns if the module still isn't communicating. The wiring, power, or module fault has to be repaired first.

Read & clear U0108 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX