U0056 — Vehicle Communication Bus D Performance

Causes

• Damaged, chafed or corroded wiring or connector on Bus D
• Poor ground or supply voltage to one or more modules on Bus D
• Faulty module transmitting excessive errors or noise onto the bus
• Missing or incorrect termination (open or shorted termination resistor)
• Water intrusion or corrosion in connectors or junctions
• Intermittent connection (loose connector, bent pin)

Symptoms

• One or more control units become unresponsive or report faults
• Multiple warning lamps or messages related to different systems
• Loss of specific functions that use Bus D (depends on vehicle option)
• Intermittent faults that clear or return with driving or vibration
• Possible reduced vehicle functionality or limp-home behavior

What to check

• Read all stored and pending U-codes and related freeze frame data
• Check battery voltage and main ground connections; ensure stable supply
• Visually inspect wiring harnesses, connectors and junction boxes for damage, corrosion or water ingress
• Check for other U-codes that identify which module(s) are not communicating
• Measure termination resistance across CAN_H and CAN_L (approx. 60 ohms with both terminations present)
• Use scan tool to attempt to communicate with modules on Bus D and note which modules respond

Signal parameters

• Idle voltages (typical HS-CAN): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive)
• Dominant state (typical HS-CAN): CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V)
• Termination resistance: ≈ 60 ohms between CAN_H and CAN_L when both terminations present
• Bus bit rates vary by model — common rates: 500 kb/s (HS-CAN), 250/125 kb/s (MS/LS-CAN); confirm with service data
• Look for excessive error frames, long periods of dominant state, or voltage spikes on the bus

Similar codes