U0025 DTC: Low Speed CAN Communication Bus (+) High

What Does U0025 Mean?

Diagnostic Trouble Code (DTC) U0025 indicates that the Low-Speed CAN Bus High (CAN+) circuit voltage is higher than the expected operating range. This abnormal voltage condition can interfere with communication between electronic control modules and may cause network communication errors.

Symptoms

• Check Engine Light or warning messages
• Multiple dashboard warning lights
• Communication errors with scan tools
• Body control system malfunctions
• Power windows or door locks may operate incorrectly
• Intermittent electrical problems
• Loss of communication with some modules

Common Causes

• CAN High wire shorted to battery voltage
• Damaged CAN wiring insulation
• Water intrusion in connectors
• Corroded or damaged terminals
• Faulty CAN transceiver inside a control module
• Incorrect electrical modifications
• Charging system voltage problems

Typical Diagnostic Flow

Battery

│

▼

Scan All Modules

│

▼

Check CAN High Voltage

Normal CAN High (+) ────────────── U0025: ────────────── ▲ High Voltage

CAN+ Voltage Too High

▼

Repair Wiring or Faulty Module

How to Diagnose U0025

• Check all stored communication DTCs.
• Measure CAN High voltage with a digital multimeter.
• Inspect the CAN harness for contact with battery power wires.
• Check connectors for corrosion or moisture.
• Disconnect modules one at a time to locate the source.
• Verify charging system voltage is within specification.

Typical CAN Bus Values

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

Estimated Repair Cost

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

Related DTCs

• U0023
• U0024
• U0026
• U0100
• U0140

Frequently Asked Questions

Can I drive with U0025?

The vehicle may operate, but communication problems can affect important electronic systems. Diagnosis is recommended.

What causes CAN High voltage to become too high?

A short to battery voltage, damaged wiring, faulty control module, or electrical charging issue can cause excessive CAN High voltage.

Will replacing the ECU fix U0025?

Not always. Wiring faults and connector problems should be checked before replacing any control module.