U0030 DTC: Vehicle Communication Bus A (+) Open

What Does U0030 Mean?

Diagnostic Trouble Code (DTC) U0030 indicates that an open circuit has been detected in the Bus A CAN High (CAN+) communication line. A broken or disconnected CAN High circuit prevents control modules from exchanging data correctly, resulting in communication failures across multiple vehicle systems.

Symptoms

• Check Engine Light illuminated
• Multiple warning lights on the dashboard
• Loss of communication with one or more control modules
• ABS, Airbag, or Stability Control warnings
• Power windows, locks, or HVAC may stop working
• Instrument cluster warning messages
• Diagnostic scan tool communication errors

Common Causes

• Open CAN High (Bus A +) wire
• Broken or damaged wiring harness
• Loose or disconnected connector
• Corroded connector terminals
• Water intrusion into electrical connectors
• Faulty Body Control Module (BCM) or another control module
• Improper aftermarket electrical modifications

Typical Diagnostic Flow

Battery

│

▼

Professional Scan Tool

│

▼

Inspect Bus A CAN High

CAN High (+) ──────────────X CAN Low (-) ──────────────

Open Circuit Detected

▼

Repair Wiring or Replace Faulty Module

How to Diagnose U0030

• Read all communication DTCs using a professional scan tool.
• Inspect the Bus A CAN High wiring for damage or breaks.
• Check connectors for corrosion, moisture, or loose pins.
• Measure CAN bus resistance with the ignition OFF.
• Verify CAN High voltage using a digital multimeter.
• Disconnect modules individually if necessary to isolate the fault.

Typical CAN Bus Values

• CAN High: approximately 2.5–3.5 V
• CAN Low: approximately 2.5–1.5 V
• Network resistance: approximately 60 Ω (Ignition OFF)
• Actual values vary by vehicle manufacturer.

Estimated Repair Cost

• CAN wiring repair: $80–300
• Connector replacement: $30–150
• Professional CAN diagnosis: $100–250
• Control module replacement: $250–1,000+

Related DTCs

• U0031
• U0032
• U0033
• U0100
• U0140

Frequently Asked Questions

Can I drive with U0030?

The vehicle may still operate, but communication failures can disable important electronic systems. The fault should be diagnosed and repaired promptly.

What is the most common cause of U0030?

The most common causes are a broken CAN High wire, loose connectors, corrosion, or a defective control module connected to Bus A.

Will clearing the DTC permanently fix U0030?

No. The code will return until the open circuit on the Bus A CAN High communication line has been repaired.