U0033 DTC: Vehicle Communication Bus A (-) Shorted to Bus (+)

What Does U0033 Mean?

Diagnostic Trouble Code (DTC) U0033 indicates that the Vehicle Communication Bus A CAN Low (CAN-) circuit is shorted to the CAN High (CAN+) circuit. When these two communication wires are electrically connected, data transmission across the CAN network becomes corrupted or stops completely, preventing electronic control modules from communicating properly.

Symptoms

• Check Engine Light illuminated
• ABS, Airbag, or Stability Control warning lights
• Multiple communication-related DTCs
• Power windows, mirrors, or door locks may stop working
• HVAC system malfunction
• Instrument cluster warning messages
• Diagnostic scan tool cannot communicate with one or more modules

Common Causes

• CAN Low wire shorted to CAN High wire
• Damaged or crushed wiring harness
• Melted wire insulation
• Water intrusion inside CAN connectors
• Loose or corroded connector terminals
• Faulty control module internally shorting the CAN network
• Improper aftermarket electrical modifications

Typical Diagnostic Flow

Battery

│

▼

Professional Scan Tool

│

▼

Inspect Bus A CAN Wiring

CAN Low (-)
──────────────

✖

CAN High (+)
──────────────

Short Circuit Between CAN- and CAN+

▼

Repair Wiring or Replace Faulty Module

How to Diagnose U0033

• Read all stored communication DTCs using a professional scan tool.
• Inspect the wiring harness for damaged or pinched wires.
• Check CAN connectors for corrosion, moisture, or loose terminals.
• Measure CAN bus resistance with the ignition OFF (approximately 60 Ω).
• Verify CAN High and CAN Low voltages with a digital multimeter.
• Disconnect control modules one at a time to isolate the short circuit.

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 specifications vary by vehicle manufacturer.

Estimated Repair Cost

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

Related DTCs

• U0030
• U0031
• U0032
• U0100
• U0140

Frequently Asked Questions

Can I drive with U0033?

The vehicle may still operate, but communication failures can disable important electronic systems, including safety and body control functions. The fault should be repaired as soon as possible.

What is the most common cause of U0033?

The most common causes are damaged CAN wiring, melted insulation allowing CAN High and CAN Low wires to touch, water intrusion, or an internally failed control module.

Will clearing the DTC permanently fix U0033?

No. Clearing the code only removes it temporarily. If the short circuit remains, the DTC will return after the CAN network performs its next self-test.