U0103 Fault Code

Long Description

Fault code U0103 is a communication fault code that is logged when the controller area network (CAN) bus loses connection with the gear selector control (GSC) module.

The CAN bus is where most of the communication is done for the computers onboard a vehicle. It allows for the various signals to be sent from one module to the next, allowing proper function of the various systems.

It is important to realize that only vehicles with automatic transmissions can suffer from this problem as there are no GSC modules on manual cars. This is because the driver’s inputs act as the gear selector, making a control module redundant.

This is a generic fault code, which means most, if not all manufacturers can suffer from it. Again, only automatic models can suffer from this code. Some of the most commonly reported brands for this code include Chevrolet, Cadillac, Ford, Mazda, and Nissan.

Other Signs of This Problem

With any control module malfunction, there can be some noticeable symptoms, and the GSC module is no different.

One of the most common signs is the Check Engine light being illuminated on the dashboard.

Other common signs are linked with the performance of the vehicle’s gearbox. This will typically be that the vehicle cannot shift at all.

In most cases, the vehicle will be stuck in the gear that it was in when communication with the GSC module was lost. However, it has also been reported that vehicles will defer back to neutral gear, making them unable to move at all.

It is also possible for gear shifting to be very erratic.

Be sure to look out for other gearbox communication-related issues like U0304, U0404, and others.

What Could Be The Problem?

When it comes to a control module malfunction, it is almost always a result of an electrical issue. These will typically be found in the wire harness between the CAN bus and the GSC module.

These issues are often loose connections or damaged wires that can cause an open or short circuit condition.

In some rarer cases, it is possible for the GSC module to have failed.

Fixes

Finding the cause of the problem is obviously the first step in fixing it. When it comes to communication fault codes, this can mean exhaustive searches through all of the relevant circuits.

One of the first steps in fixing this type of problem is to contact the vehicle manufacturer to see if there is a known problem with the GSC module.

Be sure to check the relevant connections first, as this can be easier than perusing over long lengths of wiring harness.

Thereafter, checking the wiring harness for damage or fraying is good practice.

Another step worth taking is checking the relevant fuses to ensure they are not blown.

It is always a good idea to disconnect the battery terminals before undertaking electrical troubleshooting.

Seriousness

Fault code U0103 is a moderately serious issue. While it does not necessarily pose any serious risk to the vehicle itself, it will almost always cripple driveability hugely. This can make it very important to have the issue resolved quickly.

It is strongly recommended to have the problem fixed as soon as possible.