U0031 DTC: Vehicle Communication Bus A (-) Open

What Does U0031 Mean?

Diagnostic Trouble Code (DTC) U0031 indicates that the Vehicle Communication Bus A CAN Low (CAN-) circuit has an open connection. A broken or disconnected CAN Low wire interrupts communication between electronic control modules, causing multiple systems to lose network connectivity.

Symptoms

• Check Engine Light illuminated
• ABS, Airbag, or Stability Control warning lights
• Loss of communication with one or more control modules
• Power windows, door locks, or mirrors may stop working
• HVAC system malfunction
• Instrument cluster warning messages
• Diagnostic scan tool communication failure

Common Causes

• Open CAN Low (CAN-) wire
• Broken or damaged wiring harness
• Loose, bent, or disconnected connector
• Corroded connector terminals
• Water intrusion inside CAN connectors
• Faulty BCM or other network control module
• Improper aftermarket electrical modifications

Typical Diagnostic Flow

Battery

│

▼

Professional Scan Tool

│

▼

Inspect Bus A CAN Low

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

Open Circuit Detected

▼

Repair Wiring or Replace Faulty Module

How to Diagnose U0031

• Read all stored communication DTCs.
• Inspect the Bus A CAN Low wiring for breaks or damage.
• Check connectors for corrosion, loose terminals, or moisture.
• Measure CAN bus resistance with the ignition OFF.
• Verify CAN Low voltage using a digital multimeter.
• Disconnect suspected modules one at a time 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

• U0030
• U0032
• U0033
• U0100
• U0140

Frequently Asked Questions

Can I drive with U0031?

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

What is the most common cause of U0031?

The most common causes are an open CAN Low wire, damaged wiring, loose connectors, corrosion, or a faulty control module on Bus A.

Will clearing the DTC permanently fix U0031?

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