U0206 — Lost communication with the folding upper control module

Causes

• Folding upper control module internal fault or software crash
• Power supply fault (blown fuse, bad ignition feed, low battery)
• Poor or corroded connector or pin at the module
• Open/short in CAN wiring or shield damage
• Missing or incorrect termination on the CAN bus
• Body control module (BCM) or gateway hardware/software issue

Symptoms

• Folding roof (upper) does not operate or operates intermittently
• Roof-related controls show inoperative or 'service' warnings on the instrument cluster
• Diagnostic tool cannot communicate with the folding upper control module
• Other modules report related U-codes or multiple network communication faults
• Stored event data showing loss of messages on the roof module’s CAN channel

What to check

• Scan network to confirm U0206 and note any additional U-codes and timestamps
• Check battery voltage (should be >12.4 V with key off; >13.2 V with engine running)
• Visually inspect the folding upper control module connector for corrosion, damage, or water
• Verify module fuses and live/ignition power feeds at the fusebox and module connector
• Check module ground(s) for low resistance to chassis
• Measure CAN_H and CAN_L voltages at the module connector with ignition on

Signal parameters

• Idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both centered) — dominant ~CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V
• Bus termination: ~120 ohm total (≈60 ohm between CAN_H and CAN_L at two-wire end-to-end)
• Typical data rates: 250 kb/s or 500 kb/s depending on vehicle network segment (verify OEM spec)
• Expected behavior: periodic status messages from folding upper module when awake (check OEM message IDs)
• Module supply voltage: battery/ignition feed present at pin(s) when module should be awake
• Wake/sleep signals: some modules require wake/sleep command on bus or wake input (consult wiring diagram)

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