U0006 – High Speed CAN Communication Bus (-) Open

U0006 means the car’s high-speed CAN network has lost the CAN “minus” line due to an open circuit. In plain terms, some modules cannot “hear” each other, so features can drop out or the vehicle may not start. According to factory diagnostic data, this code indicates “High Speed CAN Communication Bus (-) Open.” The real-world effect depends on which modules sit on that network segment. SAE J2012-DA U-codes stay intentionally general by design. You must confirm which module or splice leg lost communication before you blame a module.

U0006 Quick Answer

U0006 points to an open in the High-Speed CAN Bus negative (CAN-) circuit. Start with a full network scan to see which modules drop offline, then inspect CAN- wiring, splices, and connector pins in that branch.

What Does U0006 Mean?

U0006 code means a control module detected an open circuit condition on the High Speed CAN Communication Bus (-) line. In practice, the vehicle may show multiple warning lights, inoperative features, or intermittent no-start. The code does not name a failed module. It only tells you the network path for CAN- has a problem somewhere on the high-speed bus.

Officially, the definition is “High Speed CAN Communication Bus (-) Open.” The module sets U0006 when it cannot see valid high-speed CAN activity that depends on the CAN- conductor. Many modules monitor bus health by watching message traffic and error counters. That matters because a single open in one harness leg can take down several modules at once, while the rest of the bus still works.

Theory of Operation

The high-speed CAN network uses two wires, commonly called CAN+ and CAN-. Modules broadcast messages on the pair and listen at the same time. The twisted pair design cancels noise and keeps communication stable. Each module needs solid power and ground to communicate. The bus also relies on good connector pin tension and intact splices.

With U0006, the CAN- path opens somewhere in the network. A backed-out terminal, corroded splice, or chafed harness can break that conductor. When CAN- opens, the signal pair loses balance and modules log communication faults. Some modules may still appear on a scan, while others drop out. The exact pattern depends on the network topology and where the open sits.

Symptoms

U0006 symptoms usually show up as lost module communication and multiple systems acting up at once.

• Scan tool dropout: One or more modules show “no communication,” disappear from the module list, or connect intermittently during a network scan.
• Multiple warning lamps: ABS, traction control, airbag, or MIL lights may turn on together after a key cycle.
• No-start or intermittent start: The engine may crank and not start if key network modules cannot exchange security or engine data.
• Inoperative functions: Power steering assist, cruise control, stability control, or shifting strategy may disable.
• Cluster messages: The instrument cluster may show “service” warnings, blank gauges, or intermittent warning chimes.
• Harsh shifting: Some transmissions default to limp strategy when they lose CAN data from the engine or ABS modules.
• Battery draw complaint: A network that fails to sleep can cause an overnight dead battery in some cases.

Common Causes

• Open in the CAN (-) conductor (CAN Low): A break in the negative CAN line stops differential signaling, so modules drop off the high-speed network.
• Backed-out or spread terminal at a CAN connector: Poor terminal tension creates an intermittent open that looks like a bus dropout, especially over bumps.
• Corrosion or moisture in a splice pack or inline connector: Oxidation adds resistance until the CAN (-) side goes electrically “open” to the network.
• Harness damage near high-movement areas: Repeated flexing at door jambs, under seats, or engine/trans mounts can fracture the CAN (-) conductor inside intact insulation.
• Faulty terminating resistor path (one end of the bus not connected): If one terminator loses its connection to the bus due to an open, the bus resistance shifts and communication becomes unstable.
• Module connector damage pulling the bus line open: A cracked housing, bent pin, or poor pin fit at any module on HS-CAN can open the CAN (-) circuit for the entire segment.
• Aftermarket device intrusion on HS-CAN wiring: Alarm, remote start, radio, tracker, or dash cam taps can loosen or cut the CAN (-) conductor and trigger U0006.
• Power or ground issue at a key gateway module: A gateway that powers down can remove bus bias and termination reference, making the CAN (-) circuit appear open during the fault event.

Diagnosis Steps

Tools: a scan tool that can run a full network scan, view U-codes, and read freeze frame. Use a DVOM with ohms and voltage. A backprobe kit helps prevent terminal damage. Have wiring diagrams for HS-CAN routing, splice locations, and termination points. An oscilloscope helps, but you can confirm most U0006 faults without it.

1. Confirm the U0006 code and note if it shows as pending or confirmed/stored. Record freeze frame data, especially ignition state, vehicle speed, system voltage, and any related U-codes. Freeze frame shows conditions when the fault set. Use a scan tool snapshot during a drive to catch an intermittent dropout.
2. Run a complete network scan and save the report. Note which modules do not communicate and which ones do. This step tells you whether the scan tool still sees the gateway and the main HS-CAN backbone.
3. Check fuses and power distribution for the modules that dropped off the network. Verify battery state and charging voltage first. A low system voltage event can mimic a bus fault and complicate U0006 diagnosis.
4. Load-test power and ground feeds to the gateway and any non-communicating modules. Do a voltage-drop test with the circuit operating. Target less than 0.1V drop on grounds and minimal drop on power feeds under load, because high resistance can pass a static continuity test.
5. Inspect HS-CAN wiring at common failure points before you start cutting or repinning. Focus on areas with movement, heat, or water exposure. Look for crushed loom, rubbed-through insulation, prior collision repairs, and any aftermarket splices.
6. Key OFF, disconnect the battery, and let modules go to sleep if required by the OEM. Measure resistance between CAN+ and CAN- at an accessible module connector on the HS-CAN. A healthy bus reads about 60 ohms. An open on one conductor often pushes the reading toward 120 ohms or OL, depending on where you measure.
7. If resistance does not look normal, isolate the network by unplugging modules or separating connectors one section at a time. Recheck resistance after each isolation step. When the reading returns near 60 ohms, you just narrowed the fault to the last section you disconnected.
8. Key ON with the network connected, measure CAN+ to ground and CAN- to ground at the same access point. Do this with ignition ON because bias voltage only exists when the network powers up. A healthy bus typically biases both lines near 2.5V. A CAN (-) open often drives one line away from that bias or makes it unstable.
9. Perform pinpoint checks on the suspected CAN (-) path. Check continuity end-to-end on CAN (-) only after you isolate the circuit. Then do a wiggle test while watching the meter and scan tool module list. Intermittent opens often show up as a sudden resistance jump and a module dropping offline.
10. Inspect and test splice packs and inline connectors on the CAN (-) circuit. Pull gently on each wire at the splice. Check for green corrosion, water tracks, and loose crimp sleeves. Repair the splice correctly and seal it, because a poor splice repair will recreate U0006.
11. Clear codes and rerun the network scan. Road test under the same conditions shown in freeze frame. Confirm no modules drop out and U0006 does not reset as pending or confirmed.

Professional tip: If U0006 sets with a cluster of “no communication with module” codes, treat the bus like a backbone problem first. Find the point where the bus resistance changes from near 60 ohms to abnormal. That method beats guessing modules and saves hours.

Possible Fixes

• Repair the open in the High Speed CAN (-) wire using proper splicing and sealing methods, then rewrap and secure the harness to prevent repeat damage.
• Clean corrosion and restore terminal fit at the affected connector, then apply the correct terminal repair or repin procedure when tension is weak.
• Repair or replace a damaged splice pack/inline connector on the CAN (-) circuit after you confirm it changes bus resistance or drops modules offline.
• Remove or correctly rework aftermarket device connections that disturbed HS-CAN wiring, then verify network integrity with a post-repair scan report.
• Correct a power/ground supply issue at a gateway or network-critical module using voltage-drop confirmation, then retest communication stability.
• Repair wiring routing issues that cause repeat flex damage, such as inadequate strain relief near mounts or sharp bracket edges.

Can I Still Drive With U0006?

You can sometimes drive with a U0006 code, but you should treat it as a network reliability problem. U0006 means the high-speed CAN bus negative line (CAN-) has an open somewhere. When CAN- opens, modules can drop off the network without warning. That can disable systems that share data, like ABS, stability control, power steering assist, transmission shifting strategy, or engine torque management. Some vehicles fall back to a limp strategy. Others crank and start fine, then lose functions mid-drive. If the dash shows multiple warning lamps, the scan tool loses communication with key modules, or the vehicle shifts harshly, do not continue driving. Tow it instead. If the only symptom is an intermittent MIL and everything operates normally, limit driving and schedule diagnosis soon. The fault can escalate with heat, vibration, or moisture.

How Serious Is This Code?

U0006 ranges from an inconvenience to a serious safety and drivability concern. It stays minor when only one non-critical module loses data and the vehicle keeps stable operation. It becomes serious when the open on CAN- affects the main high-speed backbone. In that case, many modules can log U-codes at once, and the vehicle can lose ABS and stability control support. You can also see reduced engine power, erratic gauge behavior, or no-start depending on platform design. Ignoring the problem often increases repair cost. A small connector issue can turn into harness damage from arcing, water intrusion, or terminal fretting. Treat any repeat U0006 with multiple warning lights as high priority. Diagnose the network before replacing any module.

Common Misdiagnoses

Technicians often misdiagnose U0006 as a failed ECM, ABS module, or “bad CAN module” because the scan tool shows lost communication. That approach wastes money. The code points to an open on the high-speed CAN (-) circuit, not a confirmed failed controller. Another common mistake involves chasing the wrong symptom DTC. For example, a U0006-triggered network dropout can create throttle, transmission, and steering codes that look unrelated. Shops also skip power and ground voltage-drop tests under load. A module that browns out can mimic a bus open. Finally, people measure resistance at the DLC with modules asleep and call the network “good.” An intermittent open often appears only with harness movement, heat, or connector load. Use wiggle testing, loaded checks, and a full network topology view.

Most Likely Fix

The most common confirmed repair direction for U0006 involves finding and correcting an open in the CAN- circuit at a connector or harness junction. Focus on areas with movement or moisture. Check splice packs, module connectors, and harness routing near kick panels, under seats, and in the engine bay. The next frequent direction involves restoring clean module power and ground to a controller that repeatedly drops off the bus. After repair, confirm stability by driving under the conditions that triggered the fault. Enable criteria and time vary by vehicle. Use service information to confirm the correct road-test and recheck for pending and confirmed U-codes.

Repair Costs

Network and communication fault repairs vary by root cause — wiring/connectors are often the source, but module-level repairs or replacements can be significantly more expensive.

Last updated: April 7, 2026