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Home / DTC / U065B — Lost Communication With Left Front Mode Actuator

U065B — Lost Communication With Left Front Mode Actuator

Detailed page for trouble code U065B.

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Code

U065B

Generic U — Network/User

Lost Communication With Left Front Mode Actuator

Brand: Generic
Type: U — Network/User
Views: UK: 18 EN: 15 RU: 14
AI status
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Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between control module and left front mode actuator
  • Faulty or improperly seated connector at the actuator
  • Failed left front mode actuator (motor, gearbox, or internal electronics)
  • Blown fuse or lost ignition/switched power to actuator
  • Bad ground at actuator or control module
  • Intermittent or permanent network (CAN/LIN) fault

Symptoms

  • Loss of function for the left front mode (vent/flow/position) — actuator does not move or holds wrong position
  • Unresponsive HVAC/traction/door system functions that use the actuator (depending on vehicle)
  • Clicking or grinding noise from the left front corner when commanding mode
  • Multiple network communication-related DTCs present
  • Possible warning lamp or message on cluster related to system fault

What to check

  • Read and record U065B and any additional DTCs; capture freeze frame / vehicle state
  • Verify if actuator responds to manual or bi-directional commands from a scan tool
  • Inspect actuator connector for corrosion, bent pins, water ingress, or loose terminals
  • Check fuses and relays supplying the actuator circuit
  • Backprobe connector to measure supply voltage and ground with ignition on and while commanding actuator
  • Perform wiggle test on harness while commanding to reproduce fault

Signal parameters

  • Supply voltage to actuator: ~11–14 V with ignition on (no load)
  • Ground: near 0 V (low-impedance) at actuator ground terminal
  • Data bus: CAN_H/CAN_L idle ~2.5 V each (differential idle), or LIN bus idle pulled high to battery via pull-up — verify with scope
  • Actuator feedback signal: position potentiometer or PWM feedback (varies by design) — expected stable voltage or PWM when stationary and changing when commanded
  • Motor coil resistance: manufacturer-specific (typically low ohms); compare to service spec
  • Command frequency: if PWM-driven, typical frequencies can range from tens to a few hundred Hz — consult service data

Diagnostic algorithm

  1. Confirm code and vehicle condition: document when code set, any freeze frame, and related DTCs.
  2. Attempt to operate the left front mode actuator with a scan tool. Note response and diagnostic data (position, voltage, error status).
  3. Inspect actuator connector and wiring for obvious damage, corrosion, or moisture. Repair any physical issues.
  4. Check power and ground at the actuator connector while commanding actuators. Verify supply is present and ground is solid.
  5. If power/ground are correct but no response, check the data bus signal at the actuator connector with a scope or lab-grade meter. Look for CAN or LIN messages and proper idle levels.
  6. Wiggle the harness and connector while monitoring communication and actuator response to find intermittent faults.
  7. If data bus signals are missing at the actuator but present at the module, trace the wiring between nodes for opens/shorts. Repair as needed.
  8. If bus faults exist across multiple nodes, isolate by disconnecting suspected faulty nodes or segments and rechecking the bus.
  9. If wiring and bus are good, bench-test or substitute a known-good left front mode actuator to confirm failure of the actuator.
  10. After repair or replacement, clear codes and perform functional test and road/operational test to confirm the fault does not return. Re-scan for related codes.

Likely causes

  • Connector pin corrosion or loose terminal at the actuator
  • Damaged wiring harness (chafing, broken wires) to the left front actuator
  • Failed actuator motor or internal controller
  • Local ground or power supply fault
  • Network messaging fault caused by another node pulling the bus down

Fault status

⚠️ Status
Control module has not received expected communication/feedback from the left front mode actuator. The actuator is not reporting position or responding to commands; fault may be due to wiring, power/ground, data-bus, or actuator failure.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours
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