Network, generic

U01B8 Lost Communication With Switch Input Module B

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Carmakers that fit more than one switch input module count them A, B, C. A modular layout patented by BCS Automotive Interface Solutions shows why there can be several: a main switch module, for example for the lighting, is extended by satellite modules of different kinds, and coding contacts in the connectors tell the main unit which type is plugged in. U01B8 means the second module, B, has gone silent while the others may still work normally. The allocation is specific to each vehicle, and no maker documents U01B8 publicly, so the wiring diagram decides which buttons are affected. Check supply, ground, bus wires and connector of module B before replacing it. The driver sees only the buttons of module B fail. U04BB covers implausible data, U01B7 and U01B9 the siblings.

Likely causes

Connector of module B unplugged, loose or corroded
Missing supply voltage or ground at module B
Switch input module B faulty

Symptoms

  • Buttons served by module B without function
  • Other switch groups still working

Repair estimate

DifficultyMediumDIY possible
Parts and labour€0–400
Time0.3–2 h

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

Parts involved

switch input module bcan bus

Related codes

U04BBU01B7U01B9

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