U0006 – High Speed CAN (–) Open indicates that the negative line of the vehicle’s high-speed CAN network (CAN-L) has an open circuit. Because CAN-H and CAN-L must work together as a twisted pair, any interruption on the CAN-L side causes loss of communication between key modules such as the PCM, ABS, TCM, EPS, and airbag control unit. When CAN-L is open, data becomes unstable or stops completely, triggering warning lights and unpredictable vehicle behavior. This guide explains what U0006 means, the symptoms, causes, diagnosis steps, and the most effective repair options.
What Does U0006 Mean?
U0006 is a generic OBD-II communication code stored when a module detects that the CAN-L circuit is open or disconnected. In a properly functioning CAN bus, CAN-L sits around 1.5V during operation and works in opposition to CAN-H to create a reliable differential signal. If CAN-L is open, the differential signal collapses, causing corrupted or missing data across the network.
This fault often results in random module dropouts, intermittent no-start conditions, or the inability to communicate with multiple systems. Because modern vehicles rely heavily on CAN communication, even a small open circuit on CAN-L can cause widespread malfunctions.
Quick Reference
- OBD-II Family: U-Code (Network Communication)
- Scope: Generic
- System: High-Speed CAN Bus
- Difficulty Level: Advanced
- Estimated Repair Cost: €80–€500+
- Last Updated: 20 November 2025
Real-World Example / Field Notes
A customer’s vehicle arrived with ABS, traction control, and power steering warning lights active. The scan tool could only access a few modules, all reporting U0006. After inspecting the passenger-side kick panel, a corroded splice connecting several CAN-L wires was discovered. Moisture from a leaking windshield seal caused the corrosion, breaking continuity. Once the splice was repaired and the leak sealed, all communication returned.
Another case involved a pickup truck that intermittently stalled when hitting bumps. The PCM and BCM both logged U0006. The issue was traced to a broken CAN-L wire inside the frame rail harness where the loom had been rubbing. A soldered repair with heat shrink solved the dropout problem completely.
Symptoms of U0006 – High Speed CAN (–) Open
- Multiple warning lights: ABS, traction, power steering, airbag, and check engine.
- No communication with some modules: Scan tool cannot access entire systems.
- Intermittent stalling: PCM loses communication with crucial modules.
- No-start condition: Immobilizer or PCM cannot exchange data.
- Erratic dash behavior: Gauges drop to zero, freeze, or flicker.
- Transmission limp mode: TCM cannot receive accurate engine data.
- Loss of power steering assist: EPS system drops offline.
Common Causes of U0006
Most Common Causes
- Open circuit in CAN-L wiring
- Corroded connectors or wiring splices
- Broken harness due to vibration or abrasion
- Water intrusion inside kick panels or footwells
- Rodent damage causing cuts in CAN-L wiring
Less Common Causes
- Failed terminating resistor or module internal fault
- Incorrect aftermarket accessory wiring (radio, alarm, dashcam)
- Connector pin back-out from poor installation
- Severe corrosion in junction connectors
- Poor chassis or engine grounds affecting CAN integrity
- Battery voltage instability making the system more sensitive
Diagnosis: Step-by-Step Guide
Finding an open CAN-L circuit requires systematic testing of voltage, resistance, and wiring continuity. CAN networks are sensitive, so thorough inspection is essential.
Tools You’ll Need
Advanced scan tool, digital multimeter, oscilloscope (recommended), wiring diagrams, CAN breakout box, backprobe kit, test light, IR thermometer, and battery/alternator tester.
- Scan all modules: Identify which modules communicate normally and which do not.
- Check battery and charging system: Ensure proper voltage and no excessive AC ripple.
- Inspect wiring visually: Look for damage, corrosion, or moisture along CAN harness paths.
- Measure resistance between CAN-H and CAN-L: Expect ~60 ohms with key off. Higher values may indicate an open CAN-L circuit.
- Check CAN-L voltage: With ignition on, CAN-L should read ~1.5V. A flat 2.5V or 0V reading points to an open.
- Test continuity of CAN-L: Verify wiring continuity from module to module.
- Inspect connectors and splices: Pay special attention to known junction locations.
- Use wiggle test: Move wiring harnesses and monitor live data for communication dropouts.
- Disconnect modules one at a time: Helps isolate whether the open occurs inside a module or wiring segment.
- Use an oscilloscope: An open CAN-L line will show an incomplete or asymmetrical differential waveform.
Pro Tip: If the CAN bus shows 120 ohms instead of 60 ohms, one side of the differential pair — usually CAN-L — is open between termination points.
Possible Fixes & Repair Costs
- Repair open CAN-L wiring: Solder and heat-shrink repairs (€50–€200)
- Clean or replace corroded connectors: Connector kits (€20–€100)
- Rebuild corroded splices: Especially in floor panels and kick panels (€50–€150)
- Replace damaged harness sections: (€150–€400)
- Fix leaks causing water intrusion: Windshield, door seals, sunroof drains (€80–€250)
- Replace faulty module: If internal open circuit is found (€150–€600+)
Can I Still Drive With U0006?
Driving with U0006 is unsafe. An open CAN-L circuit can cause sudden loss of ABS, traction control, power steering, or communication with the engine or transmission. The vehicle may also stall or fail to start. Avoid driving until the fault is diagnosed and repaired, especially if multiple warning lights are present.
Related Codes
- U0073 – Control Module Communication Bus Off
- U0009 – High Speed CAN Communication Bus (-) Shorted to Bus (+)
- U0008 – High Speed CAN Communication Bus (-) High
- U0007 – High Speed CAN Communication Bus (-) Low
- U0005 – High Speed CAN Communication Bus (+) High
- U0004 – High Speed CAN Communication Bus (+) Low
- U0003 – High Speed CAN Communication Bus (+) Open
- U0002 – High Speed CAN Communication Bus Performance
- U0001 – High Speed CAN Communication Bus
Key Takeaways
- U0006 indicates an open circuit on the high-speed CAN-L wire.
- Corrosion, broken wiring, or water intrusion are the most common causes.
- Voltage testing, continuity testing, and oscilloscope checks are key to diagnosis.
- Driving with this code is unsafe due to potential module communication loss.
FAQ
Is U0006 similar to U0003?
Yes — U0003 refers to an open CAN-H line, while U0006 refers to an open CAN-L line. Both cause serious communication failures.
Can a faulty module cause U0006?
It’s less common, but possible. Most U0006 cases are wiring-related, but a module with an internal open circuit can trigger the code.
Can I drive with U0006?
It is not recommended. Loss of communication may disable brakes, steering, or transmission control.
Does U0006 always mean the wire is physically broken?
Not always — severe corrosion or a loose connector pin can create an “open” condition without visibly broken wires.
Do I need a professional to diagnose U0006?
In most cases, yes. Diagnosing CAN network faults requires advanced tools and electrical knowledge.