Network, generic

U065B Lost Communication With Left Front Mode Actuator

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The mode actuator decides where the air leaves the dash: face vents, footwell or windshield. A separate left front unit points to a layout where each front zone has its own distribution door; when the climate master gets no reply from it over LIN, U065B is stored. No maker documents this code publicly. GM's PIT5660 for the 2019 Silverado and Sierra shows the opposite case on a single mode door: the actuator lost its count of position when modes changed with vents shut and the blower on high, set no code, and relearned after about 20 key cycles. With the link down, the left outlets stay in their last mode, which matters when defrost is selected and that side cannot follow. Door range or position faults belong to codes such as B0150 or B0170.

Likely causes

Left mode actuator electronics failed
Break or short on the LIN branch to the left mode actuator
Shared actuator supply or ground missing

Symptoms

  • Left outlets keep blowing at face, floor or glass regardless of mode
  • Defrost selection does not move air to the left part of the windshield
  • Climate fault message or flashing mode indicator

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–450
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

lf mode actuatorvehicle bus wiring

Related codes

U065CU0659U0164B0150B0170

References: static.nhtsa.gov, patents.google.com, en.wikipedia.org.