Damaged, chafed or corroded wiring on the CAN high wire (short to ground or to CAN low); Poor connection or water ingress at a connector or splice on the bus, including junction points and the diagnostic socket; A faulty control unit on the bus pulling the line low internally; Low battery voltage or poor earth connections upsetting module communication; Previous accident or repair damage to wiring, or poorly fitted aftermarket electrical accessories tapped into the bus; Failed bus terminating resistance within a module, or a gateway module fault.

U0013

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
13: FaultThe specific fault in that area

What it means

U0013 means a control unit has detected that the positive (CAN high) wire of the medium speed CAN communication bus is stuck at a low voltage, or is shorted to ground or to the opposite wire. Because the module cannot send or receive messages properly on that bus, other control units may log communication faults as well. Which modules sit on the medium speed bus depends on the make and model.

Symptoms

Warning lights on the dashboard, such as ABS, airbag, engine or multiple lights at once
Instrument cluster gauges or displays not working or behaving erratically
Loss of function in modules on that bus, such as infotainment, climate control or central locking
Scan tool unable to communicate with one or more control units
Engine hard to start or running in a reduced-power mode on some models
Fault may come and go, especially over bumps or when wiring is moved

Possible causes

Damaged, chafed or corroded wiring on the CAN high wire (short to ground or to CAN low)likely
Poor connection or water ingress at a connector or splice on the bus, including junction points and the diagnostic socketlikely
A faulty control unit on the bus pulling the line low internallypossible
Low battery voltage or poor earth connections upsetting module communicationpossible
Previous accident or repair damage to wiring, or poorly fitted aftermarket electrical accessories tapped into the buspossible
Failed bus terminating resistance within a module, or a gateway module faultrare

How to diagnose

Read all stored codes from every module and note freeze frame data, checking which modules report U0013 and which report lost communication
Check battery condition and charging voltage, and inspect main earth connections, since low voltage can cause spurious bus faults
Visually inspect wiring, connectors and the diagnostic socket for damage, corrosion, moisture and recent repair work, and remove any aftermarket accessories connected to the bus for testing
Wiggle test the harness and connectors with the bus monitored, to see whether the fault appears or clears
Using the manufacturer wiring diagram, identify which modules share the medium speed bus for your model and engine
With the battery disconnected, measure resistance between CAN high and CAN low and compare with the specified value, then check each wire for short to ground and to voltage
Unplug modules on the bus one at a time, following the manufacturer procedure, to see whether the fault clears and isolate a faulty unit
Clear the codes and retest after repair to confirm the fault does not return

How to fix

Repair or replace damaged CAN high wiring, using proper soldered and sealed repairs rather than twisting or taping wires
Clean, dry or replace corroded or loose connectors and terminals
Replace a confirmed faulty control unit, then code or program it as the manufacturer requires
Restore battery health and repair poor earth connections
Remove or correctly rewire any aftermarket accessories interfering with the bus

Can I keep driving?

Medium severity

The car may still be driveable, but affected systems such as ABS, airbags or the instrument cluster may not work, so get it checked soon. If safety warning lights are on or the car loses power or will not start reliably, avoid driving it.

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