Introduction:

The U0017 diagnostic trouble code (DTC) indicates a problem with the Medium Speed Controller Area Network (MS-CAN) communication bus, specifically a signal that is registering as "High." This typically signifies a break in the communication or a fault within the CAN bus system itself. Understanding the causes and troubleshooting steps for this code is crucial for maintaining proper vehicle functionality, as the MS-CAN bus is responsible for communication between various electronic control units (ECUs).

Table: U0017 Medium Speed CAN Communication Bus (-) High

Topic Description Possible Causes
Definition The U0017 code signifies that the MS-CAN bus (-) signal voltage is abnormally high. The MS-CAN bus is a communication network used to allow various electronic control units (ECUs) within a vehicle to communicate with each other. A "High" voltage reading on the (-) line suggests a break in the circuit, a short to voltage, or a malfunctioning ECU keeping the line artificially high.
MS-CAN Bus Overview MS-CAN is a communication protocol operating at medium speed (typically 125 kbps to 500 kbps). It connects ECUs responsible for less critical functions than those on the high-speed CAN (HS-CAN) bus. Examples include body control modules (BCMs), infotainment systems, and climate control systems. The bus consists of two wires: CAN High (+) and CAN Low (-). These wires transmit differential signals, meaning the data is represented by the voltage difference between the two wires.
Symptoms The symptoms associated with a U0017 code can vary depending on which ECUs are connected to the MS-CAN bus and their functions. Common symptoms include: Malfunctioning accessories (e.g., power windows, door locks, climate control) Infotainment system issues (e.g., radio not working, navigation problems) Body control module (BCM) related faults (e.g., lighting problems, security system issues) Warning lights on the dashboard Possible engine performance issues, but less likely than with HS-CAN problems Inability to communicate with certain ECUs using a diagnostic scan tool. Open circuit in the CAN Low (-) wire: A break in the wire prevents the signal from being pulled low. Short to voltage on the CAN Low (-) wire: The wire is accidentally connected to a power source, forcing the voltage high. Faulty ECU: An ECU connected to the MS-CAN bus might be malfunctioning and driving the CAN Low (-) line high. Wiring harness damage: Damaged or corroded wiring can lead to open circuits or shorts. Loose or corroded connectors: Poor connections can interrupt the CAN bus signal. Terminating resistor failure: Although more common on HS-CAN, a faulty terminating resistor on the MS-CAN bus can disrupt signal integrity. * ECM (Engine Control Module) issue: While less common, a malfunctioning ECM could indirectly affect the MS-CAN bus if it acts as a gateway or intermediary.
Diagnostic Procedure Diagnosing a U0017 code requires a systematic approach: 1. Scan for other DTCs: Address any other DTCs present, especially those related to the CAN bus or ECUs connected to the MS-CAN. 2. Visual inspection: Carefully inspect the wiring harness, connectors, and ECUs associated with the MS-CAN bus for any signs of damage, corrosion, or loose connections. 3. CAN bus voltage testing: Use a multimeter to measure the voltage on the CAN High (+) and CAN Low (-) wires with the ignition on. Normal voltage for CAN High is typically around 2.5V to 3.5V. Normal voltage for CAN Low is typically around 1.5V to 2.5V. A significantly high voltage on the CAN Low (-) wire (e.g., close to battery voltage) indicates a problem. 4. CAN bus resistance testing: With the ignition off and the battery disconnected, measure the resistance between the CAN High (+) and CAN Low (-) wires. The resistance should be around 60 ohms (assuming two 120-ohm terminating resistors are present). An open circuit (infinite resistance) indicates a break in the wiring. * A short circuit (close to 0 ohms) indicates a short between the wires. 5. Wiring harness testing: Use a multimeter to check the continuity of the CAN Low (-) wire from one ECU to another, ensuring there are no breaks in the circuit. Also, check for shorts to ground and shorts to voltage. 6. ECU isolation: If the wiring tests are inconclusive, disconnect ECUs one at a time to see if the CAN Low (-) voltage returns to normal. This can help identify a faulty ECU that is driving the line high. 7. Oscilloscope testing: Use an oscilloscope to observe the CAN bus waveforms. A distorted or missing waveform on the CAN Low (-) wire can indicate a problem.
Common Mistakes Ignoring other DTCs: Failing to address other related DTCs can lead to misdiagnosis. Not performing a thorough visual inspection: Overlooking obvious signs of damage or corrosion. Using the wrong tools: Using the wrong multimeter or not knowing how to properly use an oscilloscope. Not disconnecting the battery: Performing resistance tests without disconnecting the battery can damage the multimeter and provide inaccurate readings. Assuming the ECU is faulty without proper testing: Replacing an ECU is expensive and should only be done after all other possible causes have been ruled out. Forgetting terminating resistors: Failing to check the terminating resistors at the end of the CAN bus. These resistors are crucial for proper signal transmission.
Related DTCs U0001 High Speed CAN Communication Bus U0002 High Speed CAN Communication Bus Performance U0100 Lost Communication With ECM/PCM "A" U0140 Lost Communication With Body Control Module * Other U-codes related to lost communication with specific ECUs on the MS-CAN bus.

Detailed Explanations:

Definition:

The U0017 code means the voltage on the CAN Low (-) wire of the MS-CAN bus is too high. This is an unusual state because normally, the CAN Low line is pulled down to represent a dominant bit during communication. A consistently high voltage suggests a problem preventing the line from being pulled low as intended.

MS-CAN Bus Overview:

The Medium Speed CAN (MS-CAN) bus provides a network for communication between different modules in a vehicle, typically those handling less critical functions than the high-speed CAN bus. It operates at a lower speed, which reduces electromagnetic interference, and is often used for body control, infotainment, and climate control systems. The MS-CAN system uses two wires, CAN High (+) and CAN Low (-), to transmit data in a differential manner.

Symptoms:

The symptoms caused by a U0017 code can vary widely. You might experience issues with your car's accessories like power windows, door locks, or climate control. The infotainment system could also be affected, leading to problems with the radio or navigation. Body control module malfunctions might manifest as lighting problems or security system issues. In some cases, warning lights on the dashboard will illuminate to alert the driver.

Diagnostic Procedure:

When diagnosing a U0017 code, start by scanning for other DTCs to see if there are any related issues. Then, perform a visual inspection of the wiring harness, connectors, and ECUs associated with the MS-CAN bus, looking for any signs of damage or corrosion. Use a multimeter to measure the voltage and resistance on the CAN High and CAN Low wires to identify any abnormalities. If necessary, test the continuity of the CAN Low wire and check for shorts to ground or voltage. In some cases, you may need to disconnect ECUs one at a time to isolate the problem or use an oscilloscope to analyze the CAN bus waveforms.

Common Mistakes:

A common mistake when diagnosing a U0017 code is ignoring other DTCs that might be related to the issue. It's also important to perform a thorough visual inspection and use the correct tools for testing. Disconnecting the battery before performing resistance tests is crucial to avoid damaging the multimeter. Don't assume that the ECU is faulty without proper testing, and remember to check the terminating resistors at the end of the CAN bus.

Related DTCs:

Several other DTCs can be related to the U0017 code, including U0001 (High Speed CAN Communication Bus), U0002 (High Speed CAN Communication Bus Performance), U0100 (Lost Communication With ECM/PCM "A"), and U0140 (Lost Communication With Body Control Module). Any U-codes related to lost communication with specific ECUs on the MS-CAN bus should also be considered.

Frequently Asked Questions:

  • What does the U0017 code mean? It means the CAN Low (-) signal on the Medium Speed CAN bus is registering a voltage that is abnormally high. This typically indicates a fault in the CAN bus wiring or a connected ECU.

  • Can I fix the U0017 code myself? Depending on your technical skills and access to diagnostic tools, you might be able to diagnose and repair simple issues like loose connections or damaged wiring. However, more complex problems may require professional assistance.

  • What are the most common causes of the U0017 code? The most common causes include open circuits in the CAN Low (-) wire, shorts to voltage on the CAN Low (-) wire, and faulty ECUs connected to the MS-CAN bus.

  • How important is it to fix the U0017 code? It's important to fix the U0017 code because it can lead to malfunctioning accessories, infotainment system problems, and other issues that affect the overall functionality of the vehicle.

  • Will a U0017 code prevent my car from starting? While less likely than with high-speed CAN issues, a U0017 code could indirectly affect engine performance or starting if critical functions reliant on the MS-CAN bus are impacted and integrated with engine management. However, it's more likely to affect accessory functions.

Conclusion:

The U0017 code indicates a problem with the MS-CAN bus, specifically a high voltage reading on the CAN Low (-) wire. A systematic diagnostic approach is essential to identify and resolve the underlying cause, ensuring proper communication between the vehicle's ECUs. Addressing this issue promptly can prevent further malfunctions and maintain the overall functionality of the vehicle.