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DTC codes / U00xx · Network wiring and bus faults / U0006

U0006High Speed CAN Communication Bus (-) Open

U0006 means the high-speed Controller Area Network (CAN) data bus has an open circuit on its negative or low-side wire, so the modules that share that bus cannot exchange messages reliably. The computer detects a missing or intermittent voltage on the CAN low line and stores this code when the bus goes silent or out of specification.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork wiring and bus faults

Symptoms you may notice

  • Multiple warning lights on the dashboard, often including the check engine light, ABS, and traction control
  • The engine may start and run normally, or it may crank but not start if the bus is completely dead
  • Erratic operation of the speedometer, tachometer, or other gauges
  • Transmission may default to limp mode or shift harshly because it cannot receive engine data
  • Often no symptoms besides the warning light when the open is intermittent or only on a non-critical segment
  • Modules such as the radio, climate control, or power windows may stop responding

Common causes, most likely first

  1. A broken or corroded wire in the CAN low circuit, often at a connector or where the harness flexes
  2. A loose or backed-out terminal in a CAN bus connector
  3. Water intrusion or corrosion in a connector or module that damages the CAN low pin
  4. A failed module that internally shorts or opens the CAN low line
  5. Aftermarket electronics improperly tapped into the CAN bus wiring
  6. A damaged splice pack or bus bar where multiple CAN low wires join

How to diagnose and fix it

  1. Scan all modules for communication codes and record which modules are offline to narrow the fault to a bus segment
  2. Inspect the CAN low wiring and connectors at each module for corrosion, loose pins, or chafing, starting with the modules that are not communicating
  3. Measure resistance from CAN low to ground and from CAN low to CAN high at the diagnostic link connector to check for an open or short
  4. Disconnect modules one at a time to see if the bus returns, isolating a failed module that is pulling the line down
  5. Repair or replace the damaged section of CAN low wire, terminal, or connector, then clear codes and verify communication
  6. If the fault remains, perform a voltage drop test on the CAN low circuit while wiggling harnesses to find an intermittent open

What a CAN low open really tells you

  • A U0006 is often set by a single failed module that holds the CAN low line open, so disconnecting modules one by one is faster than replacing wiring blindly.
  • The code does not always mean the entire bus is dead; a break on one branch can leave other modules communicating normally and still set U0006.
  • Aftermarket alarms, remote starters, or dash cameras tapped into the CAN wires are a common cause that many technicians overlook during diagnosis.
  • Corrosion inside a connector can create an open that only appears in damp weather, so a wiggle test and visual inspection of pins are essential.
  • A poor ground at a module can mimic a CAN low open because the transceiver loses its reference, so check grounds before condemning the bus wiring.

Can I keep driving with U0006?

If the vehicle starts and runs normally, you can drive it to a repair shop, but avoid long trips and expect that other systems may behave erratically. If the engine will not start or the transmission is in limp mode, do not drive and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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