U0013 — Controller Area Network (CAN) Data Bus: Medium Speed Bus(+) – Voltage Low #

Note: The code label may vary depending on the vehicle manufacturer (OEM). Below are known variations:

• CAN Communication Bus Line 2 Malfunction (Toyota, Lexus)
• CAN Bus Medium Speed (+) Circuit Low Voltage (Ford)
• CAN-Bus Medium Speed Line (+) Low Voltage (General Motors)
• CAN Data Bus, Medium Speed (+) Low (Volkswagen/Audi)

Code U0013 Overview #

U0013 is a standardized diagnostic trouble code (DTC) that relates to the Controller Area Network (CAN) bus, a vital communication system connecting different control modules in your vehicle. Specifically, this code signals a low voltage condition on the medium speed CAN bus positive line—the “+” wire responsible for data transfer between modules like the transmission, body, or infotainment systems. When this voltage drops below a defined threshold, it indicates possible wiring, connection, or component issues. If present, U0013 can disrupt communication between modules and trigger various warning lights or malfunctions. While not always catastrophic by itself, this code often points to deeper connectivity issues that shouldn’t be ignored.

Common Symptoms for Code U0013 #

When a CAN bus voltage low condition occurs, your vehicle may exhibit a range of symptoms—some subtle, others more pronounced. Because the medium speed bus handles non-essential but important systems, failures can be inconvenient or even affect drivability.

• Illuminated check engine light or other warning indicators (ABS, traction, airbag, etc.)
• Intermittent or complete loss of communication with one or more control modules
• Malfunctioning or inoperative instrument cluster displays
• Non-working audio, HVAC, or body control features (e.g., power windows, locks)
• Erratic shifting or transmission performance (in some cases)
• Unexpected battery drain (if modules remain active)

Probable Causes for Code U0013 (Most to Least Common) #

Several factors can trigger a CAN bus voltage low code. Some are more common than others, but all should be investigated methodically. The following list is ordered by frequency based on field experience:

1. Corroded or damaged wiring/connectors on the medium speed CAN bus
2. Water intrusion at connectors or junctions (especially in door sills or under carpets)
3. Pinched, chafed, or shorted wiring resulting from prior repairs or impacts
4. Faulty control module drawing down the bus voltage
5. Poor ground connections or loose battery terminals
6. Aftermarket installations (alarm systems, remote starters, audio upgrades) interfering with CAN wiring
7. Internal failure of a body, gateway, or network management module

Step-by-Step Diagnostic Procedure for U0013 #

Diagnosing a U0013 CAN bus issue requires patience and a systematic approach. Rushing can lead to misdiagnosis and costly parts swapping. Follow these steps:

• Visual inspection: Examine CAN wiring harnesses, connectors, and visible grounds for corrosion, pinched wires, or water damage.
• Battery and ground check: Ensure the battery is fully charged and all ground connections are clean and tight.
• Scan for additional DTCs: Use a professional scan tool to check all modules for related communication or voltage codes.
• Wiggle test: Gently move harnesses and connectors while observing live CAN bus voltages or module communication; note any changes.
• Measure CAN voltages: Using a multimeter, check voltage on the CAN+ line (typically 2.5–3.5V with ignition ON). Abnormal readings indicate wiring or module faults.
• Isolate affected segment: If equipped, disconnect modules one at a time to identify which area or device is loading down the bus.
• Inspect for aftermarket devices: Look for any non-OEM electronics spliced into CAN circuits and temporarily disconnect them.
• Consult OEM diagrams: Reference factory wiring diagrams for correct routing and connector locations.

Possible Repairs for U0013 #

Once the root cause for the CAN voltage low is pinpointed, repair options will depend on the specific fault. Always confirm a repair by clearing the code and verifying module communication.

• Clean or replace corroded connectors and repair damaged wiring
• Dry and reseal any area affected by water intrusion
• Replace or repair pinched/chafed harnesses
• Replace the faulty control module if it’s confirmed to be drawing down the bus voltage
• Tighten or renew battery and ground connections
• Remove or properly install aftermarket electronics interfering with the CAN network
• Update module software as per OEM technical service bulletins (TSBs)

Is It Safe to Drive with Code U0013? #

Driving with a U0013 code is generally not recommended. While the vehicle may still operate, the loss of communication can lead to unpredictable behavior in safety, body, or comfort systems. In some cases, critical features like airbags, ABS, or power steering may be compromised. If warning lights are present or vehicle functions are impaired, have the issue diagnosed and repaired before further driving.

Vehicles Most Commonly Affected by U0013 #

While any modern vehicle using a medium speed CAN bus can experience U0013, certain makes and models have more frequent occurrences due to design or environment:

• Ford (Fusion, Escape, F-series, Explorer)
• General Motors (Chevrolet Malibu, Silverado, Equinox, GMC Acadia)
• Toyota/Lexus (Camry, RAV4, Highlander, ES/IS series)
• Volkswagen/Audi (Passat, Jetta, A4, Q5)
• Fiat-Chrysler (Jeep Grand Cherokee, Dodge Ram, Chrysler Pacifica)

Vehicles exposed to moisture, salt, or frequent body repairs are at higher risk regardless of brand.

Common Mistakes & Best Practices for U0013 #

Misdiagnosis is common with CAN bus issues due to their complexity. Avoid these pitfalls and follow best practices for a faster, more accurate fix:

• Replacing control modules without confirming wiring integrity first
• Overlooking water intrusion and corrosion at hidden connectors
• Ignoring aftermarket devices spliced into the network
• Failing to check grounds and battery condition, which can mimic bus faults
• Not scanning all modules for related codes—some may not report U0013 directly
• Skipping OEM technical bulletins or wiring diagram verification

U0013 Fast FAQ #

Q: Can a weak battery cause a U0013 code?
A: Yes, insufficient battery voltage or poor ground connections can mimic or trigger CAN bus voltage errors. Always check battery health first.

Q: Will clearing the code fix the problem?
A: Clearing the code will only erase the warning temporarily. If the underlying cause remains, U0013 will return as soon as the fault is detected again.

If in doubt, consult a professional technician with CAN bus diagnostic experience for a thorough assessment.