Damaged or chafed wiring on the CAN bus, especially where harnesses flex or pass through tight spaces; Corroded, loose, or backed-out pins in a module connector or splice pack; A failing control module that is corrupting bus messages or pulling the bus voltage out of spec; Improperly installed aftermarket electronics tapping into the CAN bus and introducing noise or impedance faults; A shorted or open termination resistor inside one of the modules, altering bus impedance; Water intrusion into a connector or module causing intermittent signal degradation; Poor ground connection for one or more modules on the bus, leading to unstable reference voltage

DTC codes / U00xx · Network wiring and bus faults / U0029

U0029Vehicle Communication Bus A (Performance)

Q: What does code U0029 mean?

Vehicle Communication Bus A (Performance). U0029 is a generic network communication code indicating that the vehicle's main communication bus, typically the high-speed Controller Area Network (CAN), is not performing to the expected standard. The computer has detected that the bus is active but that signal quality, timing, or message integrity falls outside the manufacturer's acceptable parameters, which can disrupt communication between control modules.

U0029 is a generic network communication code indicating that the vehicle's main communication bus, typically the high-speed Controller Area Network (CAN), is not performing to the expected standard. The computer has detected that the bus is active but that signal quality, timing, or message integrity falls outside the manufacturer's acceptable parameters, which can disrupt communication between control modules.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Multiple warning lights illuminated simultaneously, often including the check engine light, ABS, and traction control
Intermittent or complete failure of dashboard gauges and instrument cluster displays
The engine may start but run poorly, or the vehicle may fail to start at all
Erratic operation of electronic features such as power windows, locks, or climate control
Often no symptoms besides the warning light if the performance degradation is minor or intermittent
Communication loss with scan tool during diagnostics, preventing access to some modules

Common causes, most likely first

Damaged or chafed wiring on the CAN bus, especially where harnesses flex or pass through tight spaces
Corroded, loose, or backed-out pins in a module connector or splice pack
A failing control module that is corrupting bus messages or pulling the bus voltage out of spec
Improperly installed aftermarket electronics tapping into the CAN bus and introducing noise or impedance faults
A shorted or open termination resistor inside one of the modules, altering bus impedance
Water intrusion into a connector or module causing intermittent signal degradation
Poor ground connection for one or more modules on the bus, leading to unstable reference voltage

How to diagnose and fix it

Connect a scan tool and record all stored codes across every module to identify which modules are offline or reporting communication faults
Inspect the CAN bus wiring for visible damage, chafing, or corrosion, paying close attention to areas near moving components and known moisture paths
Measure resistance across the CAN high and CAN low circuits at the diagnostic link connector (DLC) with the battery disconnected; a reading near 60 ohms indicates proper termination, while a significantly different value points to a wiring or termination fault
Check for aftermarket accessories wired into the CAN bus and disconnect them temporarily to see if the code clears
Perform a voltage drop test on the ground circuits for modules on the affected bus to rule out poor grounding
Use an oscilloscope to view the CAN bus waveform and identify signal integrity issues such as noise, incorrect voltage levels, or missing messages
If wiring and grounds are confirmed good, isolate modules one at a time by disconnecting them to see if bus performance returns to normal, identifying the faulty module

What Most Techs Miss on U0029

A common misdiagnosis is replacing the instrument cluster or engine control module when the real fault is a single chafed wire behind the dashboard or in the door jamb boot.
Aftermarket remote starters, alarm systems, and dash cameras tapped into the CAN bus are frequent culprits because they introduce extra capacitance and noise that degrade bus performance without setting a hard fault.
U0029 can be set by a module that is still communicating but sending malformed or out-of-timing messages, so a module that responds to a scan tool is not automatically healthy.
Low battery voltage or a failing alternator can cause bus performance codes on many vehicles because modules drop offline or reset when supply voltage sags during cranking.
A single bad termination resistor inside one module can pull the entire bus out of specification, yet the module itself may still appear to function normally in other respects.

Can I keep driving with U0029?

If the vehicle runs and drives normally with only a warning light, you can drive it cautiously to a repair shop, but avoid long trips and high-speed driving. If multiple warning lights are on, the engine runs poorly, or the vehicle fails to start, stop driving and have it towed because communication loss can affect safety systems.

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.