U0006

What it means

U0006 is the generic SAE J2012 code for an open circuit on the negative (CAN Low) side of a high speed CAN communication bus. A control unit has detected that the CAN Low line is not continuous or has lost its connection, so messages between modules cannot be exchanged reliably. The exact module that sets the code and the bus it refers to depend on the vehicle's network layout.

Symptoms

• Multiple warning lights on at once, such as ABS, airbag, engine or traction control
• Instrument cluster gauges dropping to zero or behaving erratically
• Engine cranking but not starting, or starting and stalling
• Reduced engine power or limp mode
• Scan tool unable to communicate with one or more modules
• Intermittent faults that come and go with vibration or when driving over bumps

Possible causes

• Damaged, chafed or broken CAN Low wire (open circuit) in the harnesslikely
• Corroded, loose or pushed-out pins at a connector on the CAN network, including the diagnostic socketlikely
• Poor or missing connection at a junction point or splice in the CAN Low linepossible
• Faulty or missing termination resistance, for example from an internal fault in a module that carries a terminating resistorpossible
• Internal fault in a control unit or gateway that has disconnected its CAN Low linepossible
• Previous repair or accident damage affecting harness routing or connectorsrare

How to diagnose

1. Read all stored codes from every module and note which modules report U0006 or lost communication, then record freeze frame data
2. Check the battery is healthy and the voltage is stable, as low voltage can cause spurious network faults
3. Visually inspect the harness and connectors for chafing, water ingress, corrosion, previous repair damage and loose pins, especially near the modules reporting the fault
4. Consult the wiring diagram for the specific model and identify the CAN bus layout, the junction points and the location of the terminating resistors
5. With the ignition off and power disconnected as the manufacturer advises, measure resistance between CAN High and CAN Low at the diagnostic socket and compare with the specified value for the network
6. Perform a continuity test of the CAN Low wire between the modules and junction points, wiggling the harness to reveal intermittent breaks
7. Unplug modules one at a time as the wiring diagram permits and re-test resistance to isolate a module that is affecting the bus
8. View the CAN signal on an oscilloscope if available to confirm CAN Low is missing or distorted

How to fix

• Repair or replace the open-circuit section of CAN Low wiring using proper soldered and sealed joints, keeping the twisted pair arrangement
• Clean, repair or replace corroded or damaged connectors and re-seat or replace loose terminals
• Repair the faulty junction or splice point in the network
• Replace a faulty control unit or gateway only once testing has shown it is the cause, then code or configure it as required for the vehicle
• Correct any previous poor repairs and re-secure the harness so it cannot chafe or stretch

Can I keep driving?

Nearby codes

• U0005GenericHigh Speed CAN Communication Bus (+) High
• U0007GenericHigh Speed CAN Communication Bus (-) Low