OBD2 error codes are excellent in helping you understand what's wrong with your car, but that's only true if you know what the OBD2 code means.
In this guide, we’ll continue exploring common OBD2 error codes, particularly those in the U (User Network) category.
Let’s get started!
Recap: OBD 2 Trouble Codes
We’ve looked at a handful of OBD2 U trouble codes in Part 1 here. But if this is your first time reading about trouble codes, don’t worry.
Here’s what you need to know for now:
Your car generally has two ways of warning you that there's a problem. You're probably familiar with the first, which is to flash warning lights on your car's dashboard.
Unfortunately, those lights don’t give you much information other than telling you that there’s a problem somewhere in your vehicle.
That's where the second warning comes into play: the OBD 2 trouble codes. When you connect an OBD2 code reader to your car, it'll show you codes that give you a more specific information.
OBD Trouble Code Categories
Part of why those codes paint such a clear picture of the problem is that they narrow the issue into 1 of 4 categories:
- P codes for Powertrain problems
- B for Body problems
- C for Chassis problems
- And U for User Network, Network Communication, or other Undefined errors
In doing so, the OBD2 codes save you and your mechanic lots of time and effort in finding the problem. The quicker you find the root cause, the sooner you can fix it.
Of course, you can check out our complete introduction here to understand more about onboard diagnostics, trouble codes, and how they go together.
For now, though, let’s look at more common User Network OBD2 error codes, what they mean, and what you can do about them.
Common User Network OBD 2 Error Codes and How to Fix Them
Here are four more common user network OBD 2 error codes and how to resolve them.
U0103
Affected part: This error code relates to your car's Gear Shift Control (GSC) module.
What’s likely happening: This error code will most likely appear if the GSC module fails to communicate with other modules in your car.
These modules typically communicate using the Controller Area Network (CAN) bus to send signals back and forth. So, if there is a communications failure, the fault is likely with the CAN bus.
Symptoms: The first symptom of a problem is an illuminated Malfunction Indicator Light (MIL). However, since it's an issue with the Gear Shift Control (GSC) module, your car might also fail to shift and, therefore, stay stuck in one gear (neutral, in particular).
How to fix the problem: The most common reason behind this error code is an electrical issue, like a loss of power or grounding. So, the troubleshooting process should focus on the various communication circuits in the car to look for short circuits or a lack of electrical continuity. Any damaged parts will need to be replaced.
U0104
Affected part: This error code affects the Cruise Control Module (CCM) and other modules that it communicates with.
What’s likely happening: When you see this code, it's most likely that something is stopping the CCM from communicating with your car's other modules. That means the CAN bus circuit is open, suffers a short circuit, or is shorting to ground, all of which are not good.
Although it’s rare, it’s also possible that the control module itself is faulty. So, it’s worth checking that as well.
Symptoms: This error code will trigger the Malfunction Indicator Light (MIL) to turn on. Besides that, you’ll also experience problems with the cruise control in your vehicle. For example, you likely won’t be able to set the cruise control at all.
How to fix the problem: The solution is to inspect and repair the CAN bus, particularly those leading to and from the Cruise Control Module (CCM).
U0105
Affected part: This error code affects the Fuel Injector Control Module (FICM). More specifically, the issue here is with the FICM’s communications with other modules in your vehicle.
What’s likely happening: The most likely issue here is that the FICM is failing to communicate with the rest of your car. So naturally, that can lead to performance issues with your engine.
Here, it’s also possible that the Fuel Injector Control Module (FICM) itself is faulty. However, that’s not the most likely cause.
Instead, something prevents signals from being sent back and forth from the FICM. Since the CAN bus is how these modules communicate, that’s where the problem will likely be.
Symptoms: Firstly, the Malfunction Indicator Light (MIL) will turn on. Besides that, this problem will affect the fuel injection system. That can cause the engine to crank but not turn on.
There might be a lack of power and cylinders that misfire even with the engine on.
How to fix the problem: The root of this problem is the failure of modules to communicate. So, the CAN bus is the first thing to troubleshoot. Next, troubleshoot the FICM to ensure that it’s in good working order.
U0106
Affected part: The U0106 error code indicates a lack of communication with the Glow Plug Control Module (GPCM). This issue will affect the functionality of the glow plug in diesel vehicles.
What’s likely happening: As with many communication errors, the problem is most likely with the CAN bus, i.e., the circuit that modules use to communicate. The circuit could be shorted out, shorted to ground, or faulty in different ways.
The CAN bus should be your primary focus. But if that doesn’t solve the problem, you can also check the control module for issues.
Symptoms: This problem will happen while the Malfunction Indicator Light (MIL) is turned on. Besides that, you might find that the diesel engine takes much longer to crank.
Even when the engine is running, the combustion process might not go smoothly, leading to knocking and other issues.
How to fix the problem: The solution must focus on the CAN bus and on ensuring that all modules can communicate with each other appropriately. However, if there are no problems with the CAN bus, then the module itself will likely need to be replaced.
By Ray Hasbollah