Damaged or corroded wiring on the CAN bus 'M' circuit, including open or short circuits; A failed control module that is connected to bus 'M' and is pulling the bus down; Poor electrical connections at the module connectors, such as loose pins or water intrusion; Low battery voltage or a failing charging system causing modules to drop offline; A faulty ground connection for one or more modules on the bus; Aftermarket accessories improperly tapped into the bus wiring; Internal failure of the module that sets the code, though this is less common

DTC codes / U00xx · Network wiring and bus faults / U007F

U007FControl Module Communication Bus M Off

Q: What does code U007F mean?

Control Module Communication Bus M Off. U007F indicates that a control module has lost communication on the vehicle's Controller Area Network (CAN) bus designated as 'M', which is a manufacturer-specific communication channel. The module that set this code detected that it can no longer exchange data with other modules on that bus, often due to a wiring fault, a failed module, or a power/ground issue.

U007F indicates that a control module has lost communication on the vehicle's Controller Area Network (CAN) bus designated as 'M', which is a manufacturer-specific communication channel. The module that set this code detected that it can no longer exchange data with other modules on that bus, often due to a wiring fault, a failed module, or a power/ground issue.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Multiple warning lights illuminated on the dashboard, such as ABS, airbag, or traction control
One or more electronic systems not functioning, like power windows, climate control, or instrument cluster
The engine may run poorly or not start if the affected bus carries critical powertrain data
Intermittent operation of accessories or lights that share the bus
Often no symptoms besides the warning light if the bus is not critical for basic driving
A stored U007F code with no other obvious electrical faults

Common causes, most likely first

Damaged or corroded wiring on the CAN bus 'M' circuit, including open or short circuits
A failed control module that is connected to bus 'M' and is pulling the bus down
Poor electrical connections at the module connectors, such as loose pins or water intrusion
Low battery voltage or a failing charging system causing modules to drop offline
A faulty ground connection for one or more modules on the bus
Aftermarket accessories improperly tapped into the bus wiring
Internal failure of the module that sets the code, though this is less common

How to diagnose and fix it

Perform a full scan of all modules to identify which modules are communicating and which are not, and record all codes
Check battery voltage and charging system output to rule out low voltage as the root cause
Inspect the CAN bus 'M' wiring for physical damage, corrosion, or loose connectors, especially at modules that are offline
Measure resistance on the bus lines to check for opens or shorts, and compare with manufacturer specifications
Disconnect modules one by one to see if communication is restored, isolating a faulty module
Repair or replace damaged wiring or connectors as needed, following proper repair procedures
If a module is found to be faulty, replace and reprogram it according to the manufacturer's instructions

Before you replace the module that set U007F

U007F often appears alongside other U-codes, and the module that sets it may not be the one at fault; always check all modules on the bus.
A common oversight is assuming the code points to the module reporting it, when in fact a different module on the same bus can be dragging the network down.
Water intrusion in a connector or a chafed wire harness in the trunk or door jamb is a frequent cause that visual inspection can miss without wiggling the harness.
Aftermarket alarms or radio installations that tap into the CAN bus can introduce interference or shorts that set this code.
The 'M' bus is often a low-speed or dedicated bus for body functions, so the vehicle may drive normally, but safety systems could be compromised.

Can I keep driving with U007F?

If the vehicle runs and drives without obvious issues, you can drive it to a repair shop, but avoid long trips and be aware that some safety systems may be disabled. If multiple warning lights are on or the engine runs poorly, have the vehicle towed to prevent unsafe driving conditions.

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.