U0027 DTC: Low Speed CAN Communication Bus (+) Low

What Does U0027 Mean?

Diagnostic Trouble Code (DTC) U0027 indicates that the Low-Speed CAN Bus High (CAN+) circuit voltage is lower than the expected operating range. A low CAN High voltage disrupts communication between electronic control modules, leading to network errors and malfunctioning vehicle systems.

Symptoms

• Check Engine Light illuminated
• ABS, Airbag, or Stability Control warning lights
• Loss of communication with one or more modules
• Power windows, mirrors, or door locks malfunction
• HVAC system may not function properly
• Instrument cluster warning messages
• Communication errors with a diagnostic scan tool

Common Causes

• CAN High wire shorted to ground
• Damaged or pinched wiring harness
• Loose or corroded connectors
• Water intrusion inside CAN connectors
• Faulty CAN transceiver within a control module
• Poor ground connection
• Improper aftermarket electrical modifications

Typical Diagnostic Flow

Battery

│

▼

Professional Scan Tool

│

▼

Measure CAN High Voltage

Normal CAN High (+) ────────────── U0027: ▼ ────────────── Low Voltage

CAN+ Voltage Too Low

▼

Repair Wiring or Replace Faulty Module

How to Diagnose U0027

• Read all communication DTCs using a professional scan tool.
• Measure CAN High voltage with a digital multimeter.
• Inspect the wiring harness for damage or contact with ground.
• Check connectors for corrosion, moisture, or loose terminals.
• Inspect all network ground points.
• Disconnect control modules individually if needed 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 may vary depending on the 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

• U0025
• U0026
• U0028
• U0100
• U0140

Frequently Asked Questions

Can I drive with U0027?

The vehicle may continue to operate, but communication between electronic modules may become unreliable, affecting body, safety, and convenience systems.

What is the most common cause of U0027?

The most common causes are a CAN High wire shorted to ground, damaged wiring, poor grounding, corroded connectors, or a defective control module.

Will clearing the DTC permanently fix U0027?

No. The code will return until the low-voltage condition on the CAN High circuit has been corrected.