What it means
A control module has lost communication with the alternative fuel control module. Alternative-fuel operation may be affected on vehicles equipped with that system.
How it works
The alternative fuel control module manages or reports operation of a nonstandard fuel system, such as a vehicle's fitted alternative-fuel equipment. Other modules rely on its network messages to coordinate that system. U0108 sets when a reporting module stops receiving expected messages from the alternative fuel control module.
Common causes
Most likely first.
- Module unpowered or fuse blown
- CAN wiring to module broken
- Gateway module routing CAN messages incorrectly
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules for U0108 and related network codes, and save freeze-frame details to see whether the fault is isolated to the alternative-fuel system.
- Check whether the vehicle is using or can select its alternative-fuel mode, and note any fuel-system warnings or changes in operation.
- Inspect the alternative fuel control module connector and harness for damage, corrosion, loose connections, or signs of moisture.
- Check the module's power and ground circuits, including its fuse supply, against the manufacturer's specification.
- Test the communication wiring to the module for opens, shorts, or poor connections using the vehicle wiring information.
- If its power, ground, and wiring are sound, check gateway routing and module status with vehicle-specific diagnostics.
Common fixes
- Secure or clean a loose or corroded alternative fuel control module connector.
- Repair damaged network wiring or the module's ground connection.
- Restore module power and address the cause of any blown fuse.
- Repair a gateway or network fault if testing confirms it.
- Replace or program the alternative fuel control module only after its power, ground, and communication circuits pass testing.
Can I keep driving?
If the vehicle runs normally on its available fuel mode, drive cautiously and do not rely on alternative-fuel operation until the fault is diagnosed. Stop if the engine runs poorly, stalls, or a fuel-system warning indicates unsafe operation.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.