CAN Low wire shorted to ground, chafed or damaged in the harness; Corroded, loose or water-damaged connector on the medium speed bus; Faulty module on the bus pulling the CAN Low line down internally; Poor battery condition or low supply voltage or ground fault upsetting module communication; Damage from previous repair or aftermarket accessory wiring (alarm, audio, trailer or tracker) tapped into the bus; Open or incorrect bus termination resistance within a gateway or module.

U0016

Medium Speed CAN Communication Bus (-) Low.

Generic
Network
Generic code
Medium severity

How this code is built

U: SystemNetwork
0: Defined bySAE, the same on every car
0: AreaNetwork area 0
16: FaultThe specific fault in that area

What it means

U0016 means the control unit has detected that the medium speed CAN communication bus (-) line (CAN Low) is at a voltage lower than expected, which suggests it is shorted to ground or to another low-voltage circuit. The module that sets the code sees corrupted or missing messages on that bus, so other modules may stop communicating properly. Which modules sit on the medium speed bus varies by make, model and year.

Symptoms

Multiple warning lights on the dashboard at the same time
Instrument cluster, radio or infotainment dead or behaving erratically
Loss of communication with one or more modules when scanning
Intermittent faults with climate control, central locking or electric windows
Engine or gearbox warning lights or limp mode on some models
Battery drain from modules not going to sleep

Possible causes

CAN Low wire shorted to ground, chafed or damaged in the harnesslikely
Corroded, loose or water-damaged connector on the medium speed buslikely
Faulty module on the bus pulling the CAN Low line down internallypossible
Poor battery condition or low supply voltage or ground fault upsetting module communicationpossible
Damage from previous repair or aftermarket accessory wiring (alarm, audio, trailer or tracker) tapped into the buspossible
Open or incorrect bus termination resistance within a gateway or modulerare

How to diagnose

Read all stored codes from every module and note freeze frame data; check which modules report lost communication and which are still talking
Check battery condition and charging voltage, and check main power and earth connections, as low voltage can cause communication codes
Visually inspect the wiring and connectors on the medium speed bus for chafing, water ingress, corrosion and aftermarket additions
Check the vehicle wiring diagram for your model to identify which modules and connectors are on the medium speed bus and where the termination is
With the battery disconnected, measure resistance between the CAN High and CAN Low lines at the diagnostic socket and compare with the manufacturer specification
Check CAN Low for a short to ground and to other circuits, then unplug modules one at a time to see whether the fault clears and isolates the faulty module
Use an oscilloscope to view the CAN Low and CAN High waveforms and confirm the voltage levels and signal shape
After repair, clear codes and recheck that all modules communicate and that the code does not return

How to fix

Repair or replace the damaged section of CAN Low wiring, using proper soldered or crimped and sealed repairs as specified by the manufacturer
Clean, repair or replace corroded or damaged connectors and terminals
Replace a faulty module confirmed to be pulling the bus low, then code and configure it as required
Remove or correctly rewire any aftermarket accessory connected to the bus
Restore battery condition and repair any power or earth supply faults

Can I keep driving?

Medium severity

The car may be driveable, but loss of communication can affect warning systems, and on some models engine, gearbox or braking-related functions. Have it diagnosed soon, and stop driving if safety-related warning lights are on or the car enters limp mode.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.