U0029 DTC: Low Speed CAN Communication Bus Performance

What Does U0029 Mean?

Diagnostic Trouble Code (DTC) U0029 indicates that the Low-Speed CAN (Controller Area Network) communication bus is operating outside its expected performance range. Unlike an open or short circuit fault, this code means the network is functioning but communication is slow, unstable, delayed, or corrupted between one or more control modules.

Symptoms

• Check Engine Light illuminated
• Multiple warning lights on the dashboard
• Intermittent communication with control modules
• Power windows, mirrors, or door locks operate erratically
• HVAC system responds slowly or intermittently
• Scan tool communication may be delayed
• Random network-related DTCs

Common Causes

• Weak or unstable CAN communication signal
• High resistance in the CAN wiring
• Loose or corroded connectors
• Water intrusion into CAN connectors
• Failing Body Control Module (BCM)
• Faulty CAN transceiver inside a control module
• Low battery voltage or charging system problems
• Improper aftermarket electrical accessories

Typical Diagnostic Flow

Battery & Charging System

│

▼

Scan All Modules

│

▼

Inspect CAN Wiring & Connectors

CAN High (+) ───────────── ⇄ Unstable Data ⇄ CAN Low (-) ─────────────

Network Performance Problem

▼

Repair Wiring or Replace Faulty Module

How to Diagnose U0029

• Read all stored communication DTCs.
• Inspect CAN wiring for damage, corrosion, or loose connectors.
• Measure CAN bus resistance (approximately 60 Ω with ignition OFF).
• Check CAN High and CAN Low voltages.
• Verify battery and charging system voltage.
• Disconnect suspected modules individually to locate the source of network instability.

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
• Actual specifications vary by vehicle manufacturer.

Estimated Repair Cost

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

Related DTCs

• U0025
• U0026
• U0027
• U0028
• U0100

Frequently Asked Questions

Can I drive with U0029?

Yes, but intermittent communication failures may affect body electronics, safety systems, and vehicle convenience features. The fault should be diagnosed promptly.

What is the most common cause of U0029?

The most common causes are poor CAN wiring connections, high circuit resistance, low battery voltage, corroded connectors, or a failing control module.

Will clearing the DTC permanently fix U0029?

No. If the communication performance problem still exists, the code will return after the network performs another self-test.