U0108: Lost Communication With Alternative Fuel Control Module
What to do
The vehicle will run on petrol and stop switching to gas, so expect the changeover not to happen and the gas gauge to stop reading. It will drive normally on petrol — the fallback here is a complete working fuel system, which makes this one of the milder faults of its type.
If the gas system was fitted after the car was built rather than by the manufacturer, mention that first. Conversions splice into the vehicle's wiring and its data network, and a poorly made joint there is a common cause both of this code and of unrelated network faults elsewhere on the car. The installer is often better placed than a general workshop to trace their own wiring.
What this code means
The alternative fuel control module has stopped being heard from. The general reasoning is at U0100.
This module manages a second fuel system — liquefied petroleum gas, compressed natural gas, or a bi-fuel conversion — and decides when the vehicle runs on it rather than on petrol. Losing communication normally means the vehicle reverts to petrol and stays there, which is a sensible default and is what a driver will notice: the changeover never happens, the gas gauge stops working, and running costs go up.
On a converted rather than factory-built vehicle this is worth extra attention. Aftermarket conversions splice into the vehicle's wiring and its network, and the quality of that work varies enormously. A conversion is therefore a leading suspect for network faults generally on such a vehicle — not only for its own codes but for other modules' too, since a poorly made splice affects everything on the bus.
The practical failure is benign because the fallback is a complete, working fuel system. That is unusual in this family and worth saying: most lost communication codes remove a capability, and this one removes a choice.
Likely causes
Start here
- Corroded or loose connector · easy
- Poor wiring splice in an aftermarket installation · moderate
- Damaged data bus wiring · moderate
Less common
- Failed power or earth supply to the module · moderate
- Failed alternative fuel control module · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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