U0013 Medium Speed CAN Communication Bus (+) Low Voltage

U0013 Medium Speed CAN Communication Bus (+) Low Voltage is a diagnostic trouble code that indicates the vehicle's Medium Speed CAN (Controller Area Network) communication system has detected an abnormally low voltage on the CAN High (+) communication line.

The CAN network is the communication system that allows different electronic control modules in the vehicle to exchange data. Modern vehicles use CAN communication for many systems, including the engine control module, transmission control module, ABS module, airbag system, body control module, and various comfort electronics.

Under normal operating conditions, the CAN High (+) line operates within a specific voltage range. When the voltage drops below the expected level, communication between modules may become unreliable, causing network errors and multiple electronic system malfunctions.

When a control module detects this condition, it stores the U0013 fault code.

This fault is commonly caused by a CAN High wire shorted to ground, damaged wiring, faulty control modules, connector problems, water intrusion, or electrical system faults.

What Does U0013 Medium Speed CAN Communication Bus (+) Low Voltage Mean?

The CAN communication system uses two main wires:

• CAN High (+)

• CAN Low (-)

These two wires work together to transmit digital messages between vehicle modules.

The CAN High wire normally operates at a specific voltage level during communication. If the voltage becomes too low, the communication signal may become distorted or interrupted.

Possible causes include:

• CAN High wire shorted to ground

• Damaged CAN wiring

• Faulty control module

• Corroded connectors

• Water damage

• Battery or electrical system problems

What Is the Medium Speed CAN Bus?

Modern vehicles often use multiple CAN networks operating at different speeds.

The Medium Speed CAN bus is generally used for systems that require reliable communication but do not need extremely high-speed data transfer.

It may connect modules such as:

• Body control modules

• Climate control systems

• Door modules

• Lighting systems

• Comfort and convenience modules

• Interior electronic systems

The exact modules connected to the Medium Speed CAN network depend on the vehicle manufacturer.

How Does the CAN Communication System Work?

The CAN network allows many electronic control modules to communicate through shared wiring.

Examples of CAN communication include:

• ABS module sending vehicle speed information

• Body module controlling lighting systems

• Engine module receiving data from other vehicle systems

• Transmission module sharing operating information

Each module sends and receives digital messages through the CAN bus.

If CAN High voltage becomes too low, communication messages may not be correctly transmitted.

Symptoms of U0013

Symptoms depend on which modules are affected by the communication fault.

Check Engine Light and Warning Lights

The vehicle may display:

• Check Engine Light

• ABS warning light

• Airbag warning light

• Stability control warning

• Transmission warning light

Communication Problems Between Modules

Possible symptoms include:

• Multiple communication fault codes

• Some control modules not responding

• Diagnostic scanner unable to communicate with certain systems

Electrical System Malfunctions

Drivers may notice:

• Incorrect dashboard information

• Random warning messages

• Electronic features working incorrectly

Starting Problems

If important modules cannot communicate, possible issues include:

• No-start condition

• Delayed starting

• Immobilizer communication problems

Transmission Problems

CAN communication faults may cause:

• Harsh shifting

• Transmission warning messages

• Limited transmission operation

Intermittent Electronic Problems

Some vehicles may experience:

• Random resets

• Temporary warning lights

• Faults that appear and disappear

Common Causes of U0013

Several electrical problems can cause low voltage on the CAN High line.

CAN High Wire Shorted to Ground

One of the most common causes is the CAN High wire contacting vehicle ground.

Possible causes include:

• Damaged wire insulation

• Wiring harness damage

• Incorrect electrical repairs

• Wire rubbing against metal components

Damaged CAN Wiring

The communication harness may be damaged by:

• Cuts

• Crushed sections

• Heat exposure

• Incorrect routing

• Physical wear

Faulty Control Module

A defective module may pull the CAN High voltage lower than normal.

Possible faulty modules include:

• Body control module

• ABS module

• Transmission control module

• Engine control module

• Door control modules

Corroded Connectors

Connector problems may include:

• Moisture intrusion

• Rust

• Loose terminals

• Poor electrical contact

Water Damage

Water entering electronic components can cause:

• Short circuits

• Connector corrosion

• Communication failures

Common affected areas include:

• Fuse boxes

• Control module housings

• Door connectors

• Interior wiring areas

Aftermarket Electrical Equipment

Incorrectly installed accessories may interfere with CAN communication.

Examples include:

• Alarm systems

• Remote starters

• Multimedia systems

• Tracking devices

Battery and Charging System Problems

Electrical supply problems may affect CAN communication.

Possible causes include:

• Weak battery

• Charging system faults

• Poor electrical connections

How Is U0013 Diagnosed?

Proper diagnosis requires checking the CAN network, wiring, and connected modules.

Check for Additional Fault Codes

A diagnostic scan should identify:

• Communication-related codes

• Modules that cannot communicate

• Network problems

Additional U-codes can help locate the affected area.

Check CAN Bus Voltage

Technicians measure:

• CAN High voltage

• CAN Low voltage

• Voltage changes during communication

Lower-than-normal CAN High voltage may indicate a short to ground or module problem.

Inspect CAN Wiring

The wiring harness should be checked for:

• Damaged insulation

• Short circuits

• Melted sections

• Previous repair damage

Inspect Connectors

Electrical connectors should be checked for:

• Corrosion

• Water damage

• Bent pins

• Loose terminals

Disconnect Modules to Locate the Fault

Technicians may disconnect control modules individually to identify whether one module is causing the low voltage condition.

Check Battery and Charging System

The vehicle electrical system should be tested to ensure low voltage is not affecting CAN operation.

How Is U0013 Fixed?

The repair depends on the actual cause of the CAN communication problem.

Repair CAN Wiring

Possible repairs include:

• Repair damaged wires

• Replace damaged harness sections

• Restore proper insulation

Repair or Replace Connectors

Repairs may include:

• Cleaning corrosion

• Repairing terminals

• Replacing damaged connectors

Replace Faulty Control Modules

If a module is internally causing the CAN voltage problem, replacement may be necessary.

Repair Water Damage

Any water leaks or moisture sources should be corrected.

Remove Incorrect Aftermarket Equipment

Improper electrical accessories may need repair or removal.

Repair Battery and Charging Problems

Battery, alternator, or electrical connection problems should be corrected.

After repairs:

1. Clear all fault codes.

2. Verify communication between modules.

3. Check CAN network operation.

4. Perform a road test.

5. Confirm that U0013 does not return.

Can You Drive With U0013?

Driving with U0013 may be possible, but it depends on which systems are affected.

Possible risks include:

• Loss of communication between safety systems

• ABS or stability control problems

• Transmission issues

• Starting problems

• Unexpected electronic failures

If multiple warning lights appear or important systems stop working, the vehicle should be inspected as soon as possible.

Is U0013 a Serious Code?

U0013 is generally considered a serious communication system fault.

A CAN bus voltage problem can affect multiple vehicle systems simultaneously. Since modern vehicles depend heavily on communication between electronic modules, this fault can create safety and reliability concerns.

Prompt diagnosis is recommended.

How to Prevent U0013

Regular electrical maintenance can help prevent CAN communication problems.

Protect Wiring Harnesses

Avoid:

• Damaging wiring during repairs

• Incorrect electrical modifications

• Poor cable routing

Keep Connectors Clean and Dry

Prevent:

• Water intrusion

• Corrosion

• Loose electrical connections

Install Accessories Correctly

Aftermarket electronic equipment should be installed properly to avoid CAN interference.

Maintain Battery and Charging System

Stable voltage helps protect vehicle communication networks.

Repair Electrical Problems Early

Small wiring problems can develop into major CAN communication failures.

Final Thoughts

U0013 Medium Speed CAN Communication Bus (+) Low Voltage indicates that the vehicle has detected an abnormally low voltage condition on the CAN High communication line.

The most common causes include:

• CAN High wire shorted to ground

• Damaged CAN wiring

• Faulty control modules

• Corroded connectors

• Water damage

• Battery or charging system problems

• Incorrect electrical installations

A complete inspection of the CAN network, wiring harnesses, connectors, control modules, and vehicle electrical system is required to restore reliable communication between electronic systems.