U0007 – High Speed CAN (–) Low means the negative side of the high-speed CAN communication network (CAN-L) is operating at a lower voltage than normal. Because CAN-H and CAN-L work together as a twisted pair to carry data between modules, a low CAN-L signal disrupts communication across the network. This may cause warning lights, stalling, loss of steering assist, or intermittent no-start conditions. Although the vehicle may continue to run, a low CAN-L signal can lead to unpredictable and unsafe behavior. This guide explains what U0007 means, the symptoms, causes, diagnosis steps, and the most effective repairs.
What Does U0007 Mean?
U0007 is a generic OBD-II communication code triggered when the CAN-L circuit voltage is lower than expected. Under normal conditions, CAN-L should operate around 1.5V during communication. If the line is pulled too low due to corrosion, a partial short-to-ground, or a failing module, the ECU detects an abnormal voltage and records U0007.
This fault creates unstable network messages, causing modules to drop offline or revert to failsafe modes. Because modern vehicles rely on the high-speed CAN bus for engine management, safety systems, and chassis control, even a minor CAN-L voltage issue can create 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–€550+
- Last Updated: 20 November 2025
Real-World Example / Field Notes
A vehicle arrived with intermittent steering loss, ABS and traction lights, and random stalling. Diagnostic scans revealed U0007 stored in the PCM, ABS, and EPS modules. Testing showed CAN-L voltage fluctuating around 0.6V instead of the expected 1.5V. The issue was traced to a partially crushed wiring harness above the transmission. Repairing the damaged section restored full communication.
Another case involved a crossover SUV with occasional no-start conditions. U0007 appeared whenever it rained. Moisture had entered the driver-side footwell and corroded a CAN junction connector, lowering CAN-L voltage. Cleaning the connector and fixing the leak completely resolved the issue.
Symptoms of U0007 – High Speed CAN (–) Low
- Multiple warning lights: ABS, traction, EPS, airbag, or check engine.
- Intermittent stalling: PCM loses critical communication.
- No-start or delayed start: Immobilizer or PCM data corrupted.
- Gauges behaving erratically: Cluster flickering, resetting, or freezing.
- Loss of steering assist: EPS module may go offline.
- Transmission limp mode: TCM unable to receive engine/load information.
- Intermittent module communication failures: Scan tool cannot access all modules.
Common Causes of U0007
Most Common Causes
- Short-to-ground on CAN-L wiring
- Corroded connector pins reducing voltage
- Damaged harness from abrasion, heat, or vibration
- Faulty module pulling the CAN-L line low
- Water intrusion in footwells, kick panels, or engine bay
Less Common Causes
- Aftermarket accessories interfering with CAN wiring
- Poor chassis grounding causing voltage instability
- Rodent-chewed wiring creating partial shorts
- Termination resistor faults causing voltage imbalance
- Overloaded circuits near the CAN wiring bundles
Diagnosis: Step-by-Step Guide
Diagnosing U0007 requires careful electrical testing. Because CAN faults can be hidden inside harnesses, patience and methodical testing are essential.
Tools You’ll Need
Advanced scan tool, multimeter, oscilloscope (recommended), wiring diagrams, CAN breakout box, backprobe pins, test light, and battery/charging system tester.
- Scan all modules: Determine which modules report U0007 to identify affected network branches.
- Check battery and alternator health: Low voltage or excessive AC ripple can worsen CAN issues.
- Inspect wiring visually: Look for crushed, melted, or corroded wiring along CAN paths.
- Measure CAN-L voltage: With ignition on, expect ~1.5V. Anything significantly lower points to wiring or module faults.
- Check CAN-H and CAN-L resistance: With ignition off, measure 60 ohms across the pair. Values above 60 suggest an open or partial open affecting CAN-L.
- Inspect connectors and splices: Look for moisture, bent pins, or corrosion.
- Perform continuity testing: Trace CAN-L wiring for breaks or high resistance sections.
- Unplug modules one at a time: If CAN-L voltage returns to normal, that module is likely dragging the line low.
- Use wiggle test: Move wiring looms while monitoring live CAN data for dropouts.
- Analyze waveform with oscilloscope: Low amplitude or flat-lined CAN-L confirms the fault.
Pro Tip: A CAN-L voltage stuck near 0V almost always indicates a short-to-ground — usually from chafed wiring at a bracket or metal edge.
Possible Fixes & Repair Costs
- Repair shorted CAN-L wiring: €50–€200
- Clean or replace corroded connectors: €20–€100
- Replace damaged wiring harness sections: €150–€400
- Remove or correct faulty aftermarket wiring: €50–€150
- Fix water intrusion sources: €80–€250
- Replace failing module pulling CAN-L low: €150–€600+
Can I Still Drive With U0007?
Driving with U0007 is not recommended. Low CAN-L voltage can cause sudden loss of ABS, traction control, power steering, or critical engine communication. Symptoms may start intermittently but can worsen quickly. If multiple warning lights are illuminated, avoid driving until repairs are completed.
Related Codes
- U0073 – Control Module Communication Bus Off
- U0009 – High Speed CAN Communication Bus (-) Shorted to Bus (+)
- U0008 – High Speed CAN Communication Bus (-) High
- U0006 – High Speed CAN Communication Bus (-) Open
- 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
- U0007 means the CAN-L line voltage is too low, disrupting communication.
- Corroded connectors, shorts-to-ground, and module failures are common causes.
- Proper diagnosis requires voltage, resistance, and waveform testing.
- Driving with this code may be unsafe due to loss of critical module communication.
FAQ
Is U0007 the same as U0006?
No. U0006 means CAN-L is open; U0007 means CAN-L voltage is low. Both disrupt the CAN network but have different causes.
Can a failing module trigger U0007?
Yes. A defective module can pull the CAN-L line low internally, especially if its transceiver fails.
Can I drive with U0007?
It’s unsafe. Loss of communication may cause stalling or loss of steering or brake communication.
Does U0007 always mean a wiring short?
Most often, yes. But corroded connectors or poor grounds can also lower CAN-L voltage.
Do I need professional equipment to diagnose U0007?
In most cases, yes. CAN network faults require voltage, resistance, and waveform testing beyond basic tools.