Network, generic

U01B9 Lost Communication With Switch Input Module C

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Module C is the third switch input module. Such units often hang off a sub-bus: a Yazaki patent on door electronics shows a door unit that takes commands from CAN and forwards them over a LIN sub-bus to local nodes such as switches, window lift and mirror. When module C drops off, the receiver logs U01B9 and normally treats the affected switch states as released, a safe default. No manufacturer documents this code publicly, so only the vehicle's own wiring diagram reveals which buttons and which bus segment belong to C. Because only operating elements are concerned, the MIL stays off. A wire broken where the harness moves, at a door hinge, seat rail or steering column, is a likely cause. U04BC handles invalid content from C.

Likely causes

Wire broken in a moving harness section (door hinge, seat rail, steering column)
Fault in the unit that hosts the sub-bus of module C
Switch input module C faulty

Symptoms

  • Buttons served by module C ignored
  • Fault appears or disappears when moving a door, seat or the steering wheel

Repair estimate

DifficultyMediumDIY possible
Parts and labour€0–400
Time0.5–2.5 h

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

Parts involved

switch input module ccan bus

Related codes

U04BCU01B7U01B8

References: patents.google.com, patents.google.com.