U0018: Medium Speed CAN Communication Bus (-) shorted to Bus (+)

This code means that there is a short circuit in the medium speed CAN communication bus. The medium speed CAN communication bus is a network of wires and modules that allows different parts of your vehicle to communicate with each other. For example, the medium speed CAN communication bus can connect the engine, the transmission, the brakes, the airbags, and the radio.

A short circuit is when two wires touch each other and create a connection that is not supposed to be there. This can cause a problem for the medium speed CAN communication bus and affect the performance and safety of your vehicle. In this article, we will explain what causes a short circuit in the medium speed CAN communication bus, how to diagnose it, how to fix it, and how to prevent it.

What are the Symptoms of a Medium Speed CAN Communication Bus Short Circuit?

The symptoms of a medium speed CAN communication bus short circuit can vary depending on the vehicle make and model. However, some common symptoms include:

• Illuminated warning lights: You may see one or more warning lights on your dashboard, such as the check engine light, the ABS light, the airbag light, or the radio light. These lights indicate that there is a problem with the system that is connected to the medium speed CAN communication bus.
• Reduced performance: You may notice that your vehicle does not run as smoothly or as fast as it used to. You may also experience problems with shifting gears, braking, steering, or starting the engine. These problems are caused by the short circuit interfering with the signals that are sent and received by the medium speed CAN communication bus modules.
• No communication: You may find that some of the features or functions of your vehicle do not work at all. For example, you may not be able to use the radio, the air conditioning, the cruise control, or the navigation system. These features or functions are controlled by the medium speed CAN communication bus modules, and if they cannot communicate with each other, they will not work.

If you experience any of these symptoms, it is important to have your vehicle checked by a qualified mechanic as soon as possible. Driving with a medium speed CAN communication bus short circuit can be dangerous and may cause further damage to your vehicle.

What are the Causes of a Medium Speed CAN Communication Bus Short Circuit?

There are several possible causes of a medium speed CAN communication bus short circuit. Some of the most common causes are:

• A short circuit between the medium speed CAN communication bus (-) and (+) wires: The medium speed CAN communication bus has two wires, one negative (-) and one positive (+). These wires carry the signals that are sent and received by the medium speed CAN communication bus modules. If these wires touch each other, they will create a short circuit that will disrupt the communication and the power supply of the medium speed CAN communication bus. This can happen if the wires are damaged, corroded, or loose.
• A faulty medium speed CAN communication bus module: The medium speed CAN communication bus modules are the devices that are connected to the medium speed CAN communication bus wires. They are responsible for sending and receiving the signals that control the different parts of your vehicle. If one of the modules is faulty, it may send or receive the wrong signals, or no signals at all. This can cause a short circuit in the medium speed CAN communication bus and affect the other modules that are connected to it.
• A faulty ECU or other electronic control unit: The ECU or the electronic control unit is the main computer of your vehicle. It monitors and controls the different systems of your vehicle, such as the engine, the transmission, the brakes, and the airbags. It is also connected to the medium speed CAN communication bus and communicates with the medium speed CAN communication bus modules. If the ECU or another electronic control unit is faulty, it may send or receive the wrong signals, or no signals at all. This can cause a short circuit in the medium speed CAN communication bus and affect the other modules that are connected to it.
• Damaged or corroded medium speed CAN communication bus wiring: The medium speed CAN communication bus wiring is the bundle of wires that connects the medium speed CAN communication bus modules to each other and to the ECU or other electronic control units. If the wiring is damaged, corroded, or loose, it may cause a short circuit, an open circuit, or a poor connection in the medium speed CAN communication bus. This can prevent the medium speed CAN communication bus modules from communicating with each other and with the ECU or other electronic control units.

How to Diagnose a Medium Speed CAN Communication Bus Short Circuit?

To diagnose a medium speed CAN communication bus short circuit, you will need a scan tool that can read the DTC codes. You will also need a multimeter, a test light, and a wiring diagram of the medium speed CAN communication bus. Here are the steps to diagnose a medium speed CAN communication bus short circuit:

1. Step 1: Scan the vehicle for codes. Connect the scan tool to the diagnostic port of your vehicle and turn on the ignition. Follow the instructions on the scan tool to read the DTC codes. If you see the code U0018, it means that there is a short circuit in the medium speed CAN communication bus. You may also see other codes related to the medium speed CAN communication bus, such as U0019, U0020, U0021, or U0022. Note down all the codes and clear them from the memory.
2. Step 2: Inspect the medium speed CAN communication bus wiring for damage or corrosion. Locate the medium speed CAN communication bus wiring under the hood or under the dashboard of your vehicle. Follow the wiring from the ECU or other electronic control units to the medium speed CAN communication bus modules. Check the wires for any signs of damage, such as cuts, frays, burns, or melted insulation. Also check the wires for any signs of corrosion, such as green or white deposits, rust, or moisture. If the wiring is damaged or corroded, it may need to be repaired or replaced.
3. Step 3: Check the medium speed CAN communication bus modules for proper operation. Disconnect the electrical connectors from the medium speed CAN communication bus modules. Use the multimeter or the test light to check the power and ground supply to the modules. Also use the multimeter or the test light to check the continuity and resistance of the medium speed CAN communication bus wires. Refer to the wiring diagram of the medium speed CAN communication bus for the correct values and connections. If a faulty module or a faulty wire is found, replace it.
4. Step 4: Check the ECU or other electronic control units for proper operation. Disconnect the electrical connectors from the ECU or other electronic control units. Use the multimeter or the test light to check the power and ground supply to the units. Also use the multimeter or the test light to check the continuity and resistance of the medium speed CAN communication bus wires. Refer to the wiring diagram of the medium speed CAN communication bus for the correct values and connections. If a faulty unit or a faulty wire is found, replace it.

How to Fix a Medium Speed CAN Communication Bus Short Circuit?

To fix a medium speed CAN communication bus short circuit, you will need to replace the faulty component that is causing the problem. Depending on the cause of the short circuit, you may need to replace the medium speed CAN communication bus wiring, the medium speed CAN communication bus module, the ECU or other electronic control unit, or a combination of these. Here are the steps to fix a medium speed CAN communication bus short circuit:

• Step 1: Replace the faulty medium speed CAN communication bus wiring. Disconnect the electrical connectors from the medium speed CAN communication bus modules and the ECU or other electronic control units. Follow the wiring from the ECU or other electronic control units to the medium speed CAN communication bus modules. Repair or replace any damaged or corroded wires as needed. Reconnect the electrical connectors to the medium speed CAN communication bus modules and the ECU or other electronic control units.
• Step 2: Replace the faulty medium speed CAN communication bus module. Disconnect the electrical connectors from the medium speed CAN communication bus module. Remove the bolts or screws that secure the module to the vehicle. Remove the module and install the new one. Secure the module with the bolts or screws and reconnect the electrical connectors.
• Step 3: Replace the faulty ECU or other electronic control unit. Disconnect the electrical connectors from the ECU or other electronic control unit. Remove the bolts or screws that secure the unit to the vehicle. Remove the unit and install the new one. Secure the unit with the bolts or screws and reconnect the electrical connectors.

How to Test a Medium Speed CAN Communication Bus Short Circuit?

After repairing or replacing the wiring, modules, or units, you will need to test the system to make sure that the problem is fixed. Here are the steps to test a medium speed CAN communication bus short circuit:

1. Step 1: Clear the DTC codes and retest the system. Connect the scan tool to the diagnostic port of your vehicle and turn on the ignition. Follow the instructions on the scan tool to clear the DTC codes and retest the system. If the U0018 DTC does not return, it means that the repair was successful and the short circuit is fixed. If the U0018 DTC returns, it means that the repair was not successful and the short circuit is still present. You will need to repeat the diagnosis and repair steps until the problem is solved.
2. Step 2: Check the symptoms and the performance of the vehicle. After clearing the DTC codes and retesting the system, you should also check the symptoms and the performance of your vehicle. You should not see any warning lights on your dashboard, and your vehicle should run smoothly and quickly. You should also be able to use all the features and functions of your vehicle, such as the radio, the air conditioning, the cruise control, or the navigation system. If you notice any improvement in the symptoms and the performance of your vehicle, it means that the repair was successful and the short circuit is fixed. If you notice no improvement or worse symptoms and performance, it means that the repair was not successful and the short circuit is still present. You will need to repeat the diagnosis and repair steps until the problem is solved.

Conclusion

A medium speed CAN communication bus short circuit (DTC code U0018) is a common problem that can affect your vehicle’s performance and safety. It means that there is a problem in the network of wires and modules that allows different parts of your vehicle to communicate with each other. A short circuit can disrupt the communication and the power supply of the medium speed CAN communication bus and cause various problems for your vehicle.

The symptoms of a medium speed CAN communication bus short circuit can include illuminated warning lights, reduced performance, and no communication. The causes of a medium speed CAN communication bus short circuit can include a short circuit between the medium speed CAN communication bus (-) and (+) wires, a faulty medium speed CAN communication bus module, a faulty ECU or other electronic control unit, or damaged or corroded medium speed CAN communication bus wiring.

To fix a medium speed CAN communication bus short circuit, you will need to replace the faulty component that is causing the problem. You may need to replace the medium speed CAN communication bus wiring, the medium speed CAN communication bus module, the ECU or other electronic control unit, or a combination of these. To test a medium speed CAN communication bus short circuit, you will need to clear the DTC codes and retest the system. You will also need to check the symptoms and the performance of your vehicle.

Don’t forget to share it