Network, generic

U01B7 Lost Communication With Switch Input Module A

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

A switch input module collects a group of buttons, for instance in a door trim, steering wheel or centre console, and sends their states to other units as network messages instead of wiring every switch on its own. A patent by Eaton describes the idea: a central unit queries every switch by its address and accepts only answers whose address and state are valid. U01B7 is set when module A stops responding, so the receiver, often the body controller, treats its buttons as unknown. Which switches belong to module A is up to each carmaker; no manufacturer documents this code publicly. Typically a whole group of buttons does nothing and their indicator lamps stay dark, while all other systems keep working. U04BA is the invalid-data code; modules B and C have U01B8 and U01B9.

Likely causes

Loose connector or broken wire at the switch panel
Liquid spilled into the switch module
Switch input module A faulty

Symptoms

  • A group of buttons without function
  • Switch backlight or indicator lamps dark

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 acan bus

Related codes

U04BAU01B8U01B9U0140

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