CAN low wire shorted to a voltage supply in the harness, often from chafed or damaged insulation; Damaged, corroded or loose connector terminals on the medium speed CAN bus; Faulty control unit or gateway pulling the CAN low line high internally; Water ingress or corrosion in a connector, junction or module; Previous repair or aftermarket accessory (alarm, tracker, audio) wired into the bus incorrectly; Low battery voltage or poor power and earth supply to a module causing bus errors.

U0017

Medium Speed CAN Communication Bus (-) High.

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
17: FaultThe specific fault in that area

What it means

U0017 is a network communication code. It means a control unit has detected that the medium speed CAN bus negative line (CAN low) is stuck at a higher voltage than it should be. This is usually a short to a voltage source or a wiring fault on that bus, and it can stop modules from talking to each other.

Symptoms

Warning lights on the dash, such as ABS, airbag, engine or multiple lights at once
Instrument cluster gauges or displays behaving oddly or not working
Some systems not working, such as central locking, windows, climate control or infotainment
Scan tool unable to communicate with one or more modules
Intermittent faults that come and go with vibration or damp conditions
Car difficult to start or not starting, depending on which modules are affected

Possible causes

CAN low wire shorted to a voltage supply in the harness, often from chafed or damaged insulationlikely
Damaged, corroded or loose connector terminals on the medium speed CAN buslikely
Faulty control unit or gateway pulling the CAN low line high internallypossible
Water ingress or corrosion in a connector, junction or modulepossible
Previous repair or aftermarket accessory (alarm, tracker, audio) wired into the bus incorrectlypossible
Low battery voltage or poor power and earth supply to a module causing bus errorsrare

How to diagnose

Read all stored codes from every module and note which are current and which are history; check freeze frame data if available
Check battery condition and charging voltage, as low voltage can cause spurious network codes
Visually inspect the wiring, connectors and junctions on the medium speed CAN bus for damage, water, corrosion or recent repair work
Check for any aftermarket accessories connected to the bus and disconnect them to see if the fault clears
Using the wiring diagram for the specific model, identify the medium speed CAN bus and its connected modules, as the layout varies by make and model
Measure the voltage on the CAN low line against the manufacturer's specification, and check for a short to supply on the wire
Check bus resistance between CAN high and CAN low with the system powered down, comparing with the specified value
Unplug modules one at a time, following the manufacturer's procedure, to see if the fault disappears and so isolate a faulty unit

How to fix

Repair or replace the damaged section of wiring where the CAN low line is shorted to voltage
Clean, repair or replace corroded or damaged connectors and terminals, and fix the source of any water ingress
Replace any control unit or gateway confirmed to be pulling the bus high, then carry out any programming or coding it needs
Remove or correctly rewire any faulty aftermarket accessory connected to the bus
Repair battery, power or earth supply problems, then clear the codes and confirm the fault does not return

Can I keep driving?

Medium severity

The car may be drivable, but loss of communication can affect systems such as ABS, airbags, stability control or engine management, so have it checked soon. If the car runs poorly, safety warning lights are on or it will not start reliably, avoid driving it.

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