OBD-II trouble code
U0006: High Speed CAN Communication Bus (-) Open
The CAN-Low (negative) wire of the high-speed communication bus is open — broken, disconnected, or interrupted in the harness. Modules downstream of the break can no longer exchange data.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $100 – $800
- DIY difficulty
- Shop recommended
What does U0006 mean?
U0006 is a circuit-specific network code that means the high-speed CAN bus's negative line — usually labeled CAN-Low or CAN(-) — has gone open. An open is a break in the circuit: a cut or corroded wire, a backed-out terminal, a separated splice, or an unplugged connector. It's the mirror image of U0003, which describes the same kind of open on the CAN-High side.
High-speed CAN carries each data bit as a voltage difference between CAN-High and CAN-Low. When CAN-Low is open, the modules past the break lose the low half of that differential pair, so messages stop crossing the affected segment. The modules that notice the missing traffic store U0006, and you'll commonly see several module-specific lost-communication codes set at the same time because those modules truly dropped off the network.
Since the CAN bus links the engine computer, transmission, ABS, instrument cluster, and body modules, an open CAN-Low line can disable multiple systems at once. The car may crank but not start, fall into limp mode, or fail to communicate with a scan tool on the affected modules. U0006 is an electrical fault to be traced with a meter and wiring diagram, not solved by swapping parts.
Common causes
- Broken or cut CAN-Low wire from rodent damage, an accident, or chafing against a bracket
- Backed-out, spread, or corroded terminal at a module connector
- Separated or cold splice in the CAN-Low conductor
- Unplugged or partially seated connector after recent service
- Water intrusion and corrosion opening the circuit intermittently
- Open in a CAN-Low terminating resistor branch
- Harness damage near a connector boot where the wire flexes
Symptoms
- Multiple warning lights on at once (check engine, ABS, traction, airbag)
- Engine may crank but not start, or run in limp mode
- Gauges dead, frozen, or erratic
- Scan tool cannot reach one or more modules on the affected segment
- Several module-specific lost-communication U-codes stored together
- Symptoms that come and go with road vibration if the open is intermittent
Diagnostic steps
- 1.Record every stored code in all modules; which modules dropped off helps locate the break in the CAN-Low line.
- 2.With key off and battery disconnected, measure resistance across CAN-High and CAN-Low at the OBD port. About 60 ohms is healthy; an open branch often reads near 120 ohms or infinite.
- 3.Run continuity checks on the CAN-Low wire between connectors, segment by segment, to pinpoint the break.
- 4.Inspect connectors for backed-out, spread, or corroded terminals and reseat or repair as needed.
- 5.Wiggle-test the harness and connectors while monitoring bus communication to catch an intermittent open.
- 6.Use a wiring diagram to confirm which modules sit downstream of the suspected break and verify they lost communication.
Repair cost
$100 – $800
Diagnosis often runs $150-$300 since tracing an open along the harness is methodical. A wire or terminal repair is frequently $150-$500 depending on access. Splice or connector repairs land in the same range; a harness section buried behind the dash or under the floor pushes labor toward the high end.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.