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U0108 — Lost Communication Alternative Fuel Control Module

Generic OBD-II · all makesNetwork / communication

This generic communication code indicates the powertrain control module (PCM) has lost contact with the alternative fuel control module. It suggests a disruption in the data network rather than a mechanical engine failure. The vehicle may default to primary fuel or enter a limp mode.

Symptoms

What causes it — most likely first

1. Damaged wiring or corroded connectors

Physical damage to the harness or corrosion at the connector prevents data signals from reaching the module.

2. Loss of power or ground to module

The alternative fuel control module cannot communicate if it lacks proper electrical supply or grounding.

3. Failed alternative fuel control module

The internal electronics of the specific fuel controller may have failed, stopping all network transmission.

4. CAN bus network circuit fault

A short or open circuit on the high or low communication lines disrupts data flow across the vehicle network.

5. Module software malfunction

Corrupted calibration data within the controller may cause it to stop responding to network requests.

6. Failed PCM (rare)

Internal failure of the main engine computer is an unlikely cause for this specific communication loss code.

How it's diagnosed

  1. Perform visual inspection of wiring harness and connectors related to the alternative fuel system.
  2. Verify power and ground circuits at the alternative fuel control module connector.
  3. Measure CAN bus voltage levels at the module connector to check for network activity.
  4. Scan all other modules to see if communication loss is isolated or network-wide.
  5. Test or substitute the alternative fuel control module if power and wiring are confirmed good.
  6. Check for technical service bulletins regarding module software updates.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make

Frequently asked

Will replacing the PCM fix this code?

No, replacing the main engine computer is rarely the solution for communication loss codes like U0108.

Can I drive the vehicle with this code?

Caution is advised as the vehicle may run poorly or lack power depending on fuel system configuration.

Does this code mean the engine is damaged?

No, this indicates an electronic communication issue, not internal mechanical engine damage.

Will clearing the code fix the problem?

No, the code will return immediately if the underlying communication fault is not repaired.