Damaged wiring harness where the Bus D positive and negative wires are pinched together, often due to chafing against metal components or improper routing.; Corrosion or water intrusion in a connector that bridges the two bus lines, especially in areas exposed to moisture such as under the hood or near the floor.; A faulty control module internally shorting the bus lines together, which can occur after component failure or fluid contamination.; Aftermarket accessories improperly tapped into the bus wiring, creating a short between the data lines.; Rodent damage chewing through wire insulation and causing the conductors to touch.; A defective splice pack or junction connector where the bus wires are joined, leading to unintended contact.

DTC codes / U00xx · Network wiring and bus faults / U0063

U0063Vehicle Communication Bus D (shorted to Bus D)

Q: What does code U0063 mean?

Vehicle Communication Bus D (shorted to Bus D). U0063 is a generic network communication code indicating that the vehicle's main communication bus, designated Bus D, has a short circuit to itself, meaning the positive and negative data lines are shorted together. The computer detects this when the differential voltage between the two bus wires is near zero volts, preventing normal data exchange between modules.

U0063 is a generic network communication code indicating that the vehicle's main communication bus, designated Bus D, has a short circuit to itself, meaning the positive and negative data lines are shorted together. The computer detects this when the differential voltage between the two bus wires is near zero volts, preventing normal data exchange between modules.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Multiple warning lights illuminated on the dashboard, often including the check engine light, ABS, and airbag lights.
The engine may start but run poorly or not start at all if the short affects critical modules.
Intermittent or complete failure of communication with scan tools, preventing access to some or all control modules.
Erratic operation of electrical accessories such as power windows, radio, or climate control.
Often no symptoms besides the warning light if the short is intermittent or affects a non-essential module.
Transmission may default to limp mode or fail to shift properly due to lost communication with the powertrain control module.

Common causes, most likely first

Damaged wiring harness where the Bus D positive and negative wires are pinched together, often due to chafing against metal components or improper routing.
Corrosion or water intrusion in a connector that bridges the two bus lines, especially in areas exposed to moisture such as under the hood or near the floor.
A faulty control module internally shorting the bus lines together, which can occur after component failure or fluid contamination.
Aftermarket accessories improperly tapped into the bus wiring, creating a short between the data lines.
Rodent damage chewing through wire insulation and causing the conductors to touch.
A defective splice pack or junction connector where the bus wires are joined, leading to unintended contact.

How to diagnose and fix it

Verify the code with a scan tool that can access all modules and check for communication with each one to confirm the bus fault.
Inspect the Bus D wiring harness for visible damage, pinches, or corrosion, starting near recently repaired areas or aftermarket installations.
Disconnect the battery and measure resistance between the Bus D positive and negative terminals at the diagnostic link connector (DLC) to check for a short.
Isolate sections of the bus by disconnecting modules one at a time to see if the short disappears, identifying the faulty segment or module.
Repair any damaged wiring by soldering and sealing with heat shrink, or replace the affected harness section.
Replace any module that is found to be internally shorting the bus lines after confirming it is the source.
Clear the code and perform a road test to ensure communication is restored and the code does not return.

Common Misdiagnosis Traps for Bus D Shorts

A shorted bus can be caused by a single module failing internally, so technicians who replace wiring without testing modules may miss the real culprit.
Aftermarket alarms or remote starters are frequently tapped into the bus wiring and can create a short that only appears when the accessory is active.
The code may set intermittently due to a wire that only shorts when the vehicle hits a bump or when temperature changes cause expansion, making it hard to reproduce in the shop.
Bus D is often used for high-speed powertrain communication, so a short can disable the engine control module and cause a no-start condition that mimics a failed fuel pump or ignition system.
Some vehicles use terminating resistors at the ends of the bus; a failed resistor can cause voltage irregularities that set this code even without a true short.

Can I keep driving with U0063?

Do not drive the vehicle with an active U0063 code because the short can disable critical modules and cause unpredictable behavior or a no-start condition. If the code is intermittent and the vehicle runs normally, drive only to a repair shop at low speed and avoid rough roads.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.