U0108 Fault Code

Long Description

Fault code U0108 is a communication-related code that is logged when an issue with the alternative fuel control module has been detected. The code specifies that communication has been lost with this control module.

This is a very specialized fault code because not all vehicles have an alternative fuel system, and in turn an alternative fuel control module. These systems are used in vehicles that have alternative fuel sources like compressed natural gas (CNG), liquid natural gas (LNG) or propane.

This module needs to communicate with the various other control modules through the controller area network (CAN) bus. A loss of communication indicates this is not working properly.

Among the few vehicles that can be susceptible to this code, Dodge, Chevrolet, Ford, and VW are some of the most commonly searched alongside it.

Other Signs of This Problem

The symptoms for this issue can be fairly obvious because of the importance of any control module.

The presence of the Check Engine light is typically the most obvious symptom for most fault codes.

However, there is another more noticeable sign for this issue. In most cases, the engine will crank but not start at all.

If the vehicle does run, there will likely be very significant performance issues. These include running rough, a lack of power, and even misfires.

It is also possible for this code to cause the fuel gauge to show an incorrect level.

This code will potentially be logged with other communication system fault codes. Be sure to look out for codes like U0001 through to U0009, as well as U0100.

What Could Be The Problem?

This fault code indicates a loss of communication, which means that there is likely an electrical issue somewhere in the CAN bus circuit causing the problem.

In most communication-related instances, there are a number of common causes. An open or short circuit in the CAN bus can be one of the most likely.

It is possible for there to be a shortage to ground or power. It is also possible that there is an open circuit in either the positive or negative wires in the CAN bus.

It is possible that there are electrical faults like damaged wires somewhere in the CAN bus circuit.

Another possible cause is that one or more control modules are faulty. In this case, the alternative fuel control module and PCM are the primary suspects.

Fixes

Fixing this fault code can be difficult. In most cases, a communication fault code should be deferred to the dealership or a certified service point for the manufacturer of the vehicle because of the complexity of these systems.

It is a good idea to check for a technical service bulletin that relates to the make and model in question. This can potentially save a lot in terms of time, costs, and labor to find the issue.

The CAN bus wires need to be checked for electrical faults. Any open or short circuits need to be fixed accordingly.

If it can be determined that the PCM or alternative fuel control module are defective, they need to be replaced.

Seriousness

Fault code U0108 is a serious issue. A loss of communication with the alternative fuel control module means that the vehicle will suffer hugely in terms of performance. As mentioned, it is likely that it will be unable to even start.

It is highly recommended to have this fault code fixed immediately.