A chafed or broken CAN low wire in a door hinge area, trunk loom, or under-seat harness where flexing occurs.; Water intrusion into a connector or module on the medium-speed bus, causing corrosion and a short to ground.; A failed module on the bus that internally shorts the CAN low line, pulling the whole network down.; Loose or corroded ground connection shared by several modules, which makes the CAN low reference float or sag.; Aftermarket accessories spliced into the bus wiring, such as alarms or trailer brake controllers, creating an unintended ground path.; A damaged termination resistor inside one module, which upsets the bus voltage levels even though the wiring looks fine.

DTC codes / U00xx · Network wiring and bus faults / U0016

U0016Medium Speed CAN Communication Bus (-) Low

Q: What does code U0016 mean?

Medium Speed CAN Communication Bus (-) Low. U0016 means the medium-speed Controller Area Network (CAN) data bus has a short to ground or an open on its negative signal wire, so modules on that bus cannot exchange messages reliably. The computer detects this by monitoring the CAN low line voltage and seeing it stay outside the normal expected range instead of toggling as data is transmitted.

U0016 means the medium-speed Controller Area Network (CAN) data bus has a short to ground or an open on its negative signal wire, so modules on that bus cannot exchange messages reliably. The computer detects this by monitoring the CAN low line voltage and seeing it stay outside the normal expected range instead of toggling as data is transmitted.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Often no symptoms besides the warning light if the fault is intermittent or affects only non-critical modules.
Multiple unrelated warning lights on the dashboard, such as stability control, airbag, or transmission warnings, because several modules share the bus.
Intermittent or complete failure of features like power windows, climate control, or radio, depending on which modules sit on the medium-speed bus.
The engine may start and run normally, but some accessories or driver-assist systems stop responding.
A no-start condition if the shorted bus prevents the immobilizer or body control module from communicating.
Erratic gauge behavior or flickering interior lights when the bus voltage is pulled low.

Common causes, most likely first

A chafed or broken CAN low wire in a door hinge area, trunk loom, or under-seat harness where flexing occurs.
Water intrusion into a connector or module on the medium-speed bus, causing corrosion and a short to ground.
A failed module on the bus that internally shorts the CAN low line, pulling the whole network down.
Loose or corroded ground connection shared by several modules, which makes the CAN low reference float or sag.
Aftermarket accessories spliced into the bus wiring, such as alarms or trailer brake controllers, creating an unintended ground path.
A damaged termination resistor inside one module, which upsets the bus voltage levels even though the wiring looks fine.

How to diagnose and fix it

Scan all modules for communication codes and record which modules are offline to narrow the fault to a specific bus segment.
Inspect the medium-speed CAN wiring at known flex points, connectors, and any place an aftermarket device was installed.
Measure resistance between CAN low and ground with the battery disconnected; a reading far below normal indicates a short to ground.
Disconnect modules one at a time from the bus and recheck the code to isolate a module that is internally shorting the line.
Repair or replace the damaged section of CAN low wiring and re-seal any connector that showed water intrusion.
Clear the code and perform a full network test drive to confirm all modules communicate before returning the vehicle.

What a CAN low short really tells you

A single failed module can drag the entire medium-speed bus low, so the module that stops communicating is not always the one causing the fault.
The code often sets from an intermittent chafe that only shorts when a door, trunk, or seat moves, so a static meter test can pass while the fault is still present.
Aftermarket wiring tapped into the CAN low wire is a frequent missed cause, especially on vehicles with added alarms, cameras, or trailer harnesses.
A poor chassis ground can mimic a CAN low short because the bus reference voltage shifts, so ground integrity must be checked before condemning a module.
U0016 does not mean the entire CAN system is dead; other buses and the engine management network may continue working normally.

Can I keep driving with U0016?

The vehicle may remain drivable if only comfort features are affected, but a shorted medium-speed bus can disable safety and starting systems without warning. Avoid long trips and have the fault diagnosed promptly, especially if multiple warning lights are on or the engine will not start.

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.