U0059 — Vehicle Communication Bus D High

Generic OBD-II · all makesNetwork / communication

OBD-II code U0059 indicates that the high-speed (typically CAN-H) line of the vehicle communication bus is experiencing an electrical fault, such as a short to power or an open circuit. This disrupts communication between control modules, potentially affecting multiple vehicle systems.

Symptoms

Multiple warning lights on the dashboard (e.g., ABS, traction control, check engine)
Loss of communication with certain modules (e.g., no scan tool data from affected modules)
Vehicle may enter a limp-home mode or fail to start
Intermittent or complete loss of power steering, stability control, or other network-dependent systems
Unresponsive or erratic behavior from infotainment or driver-assistance features

What causes it — most likely first

1. Damaged or chafed wiring harness

The CAN-H wire may be shorted to power or ground due to insulation damage, often caused by rubbing against sharp edges or heat sources. Common in areas with frequent movement or vibration.

2. Corroded or loose connectors

Poor electrical connections at module connectors or splice points can cause high resistance or intermittent shorts, especially in areas exposed to moisture or road salt.

3. Faulty control module

A module with an internal short to power on the CAN-H line can trigger this code. This is less common than wiring or connector issues but possible if other causes are ruled out.

4. Blown fuse or faulty relay in the bus power supply

If the communication bus relies on a shared power supply, a blown fuse or failed relay can cause a loss of power to the CAN-H line, mimicking a short or open circuit.

5. Aftermarket modifications or improper repairs

Incorrectly installed aftermarket accessories (e.g., stereos, alarms) or improper repairs to the wiring harness can introduce shorts or opens in the CAN-H line.

6. Faulty powertrain control module (PCM/ECM)

While rare, an internal failure in the PCM/ECM affecting the CAN-H line could cause this code. This should only be considered after all other causes are thoroughly ruled out.

How it's diagnosed

Use a scan tool to confirm the code and check for additional communication-related codes (e.g., U00xx, U01xx). Note which modules are unresponsive.
Visually inspect the CAN-H wiring harness for damage, chafing, or signs of shorting (e.g., melted insulation, discoloration). Focus on areas near sharp edges, heat sources, or high-vibration zones.
Check all connectors along the communication bus for corrosion, bent pins, or loose connections. Clean or repair as needed, ensuring proper seating and retention.
Measure voltage on the CAN-H line with a multimeter. Compare readings to manufacturer specifications (typically ~2.5V nominal, with slight variations during communication). Look for shorts to power (12V) or ground (0V).
Use an oscilloscope to observe CAN-H signal waveforms. A normal signal should show clean, square-wave patterns; distortions may indicate a short or open circuit.
Isolate modules one by one (by unplugging connectors) to identify if a specific module is causing the short. Recheck for the code after each module is disconnected.
Test fuses and relays associated with the communication bus power supply. Replace if blown or faulty, and verify proper operation afterward.

Code facts & related codes

SystemNetwork / communication

StandardizationSAE generic — identical on every make

Frequently asked

Is the PCM/ECM usually the cause of U0059?

No, the PCM/ECM is rarely the cause of U0059. This code is almost always triggered by wiring, connector, or module issues. Replacing the PCM should only be considered after all other potential causes have been ruled out.

Can I drive with U0059?

Driving with U0059 is not recommended. The code indicates a serious communication fault that can disable critical systems like stability control, ABS, or power steering, increasing the risk of an accident. Have the vehicle diagnosed as soon as possible.

Why do I have multiple warning lights with U0059?

U0059 disrupts communication between control modules, so systems like ABS, traction control, or emissions may lose their ability to report status. This often triggers multiple warning lights on the dashboard.

Can a weak battery cause U0059?

A weak or failing battery can sometimes cause communication issues, but it is unlikely to trigger U0059 specifically. However, low voltage can mimic bus faults, so always check battery and charging system health during diagnosis.