A loose, corroded, or damaged connector at the Switch Input Module C or at the module that monitors it; A blown fuse or poor ground connection supplying power to the Switch Input Module C; A wiring fault in the network bus (CAN, LIN, or similar) between the module and the rest of the vehicle; A failed Switch Input Module C itself, often due to internal electronics or water intrusion; A software or configuration mismatch after battery replacement or module replacement; A faulty switch or button that shorts the module's input circuit and takes the module offline

DTC codes / U01xx · Lost communication with a control module / U01B9

U01B9Lost Communication With Switch Input Module C

Q: What does code U01B9 mean?

Lost Communication With Switch Input Module C. U01B9 is a generic communication fault indicating that a control module on the vehicle's network has lost contact with the Switch Input Module C, a device that reads switch states such as steering wheel buttons, console switches, or door-mounted controls. The computer sets this code when it expects regular status messages from that module and they stop arriving within the required time window.

U01B9 is a generic communication fault indicating that a control module on the vehicle's network has lost contact with the Switch Input Module C, a device that reads switch states such as steering wheel buttons, console switches, or door-mounted controls. The computer sets this code when it expects regular status messages from that module and they stop arriving within the required time window.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaLost communication with a control module

Symptoms you may notice

Often no symptoms besides the warning light, especially if the affected switches are rarely used
Some or all switches on the affected module stop working, such as steering wheel audio or cruise buttons
Intermittent operation of switches that may work again after the vehicle is restarted
Other unrelated warning lights or messages if the module shares a network segment with other systems
A stored code that returns immediately after clearing even when the switches feel normal

Common causes, most likely first

A loose, corroded, or damaged connector at the Switch Input Module C or at the module that monitors it
A blown fuse or poor ground connection supplying power to the Switch Input Module C
A wiring fault in the network bus (CAN, LIN, or similar) between the module and the rest of the vehicle
A failed Switch Input Module C itself, often due to internal electronics or water intrusion
A software or configuration mismatch after battery replacement or module replacement
A faulty switch or button that shorts the module's input circuit and takes the module offline

How to diagnose and fix it

Verify the code with a scan tool and record any other communication codes that may point to a shared network fault
Inspect the Switch Input Module C connectors for looseness, corrosion, or pushed-out pins, and reseat them
Check the fuse and ground for the Switch Input Module C with a multimeter or test light
Measure network bus voltage and resistance at the module connector to confirm the bus is intact
Perform a wiggle test on the harness while watching live data for the module to catch intermittent faults
If wiring and power are good, substitute a known-good module or perform a module reflash/configuration as required
Clear the code and road-test to confirm the module communicates reliably before returning the vehicle

Why a dead switch module is often a wiring fault

A single unplugged or corroded connector at the switch module can set U01B9 even though the module itself is perfectly healthy, so always inspect connectors before condemning parts.
This code can be stored by a module that is still powered and working but simply cannot hear the Switch Input Module C on the network, which means the fault may lie in a different module's transceiver.
After a battery replacement or jump-start, some vehicles lose module configuration and set communication codes like U01B9 until a relearn or configuration procedure is completed.
Water intrusion into door or console switch assemblies is a common hidden cause, especially on vehicles with sunroof drains or cowl leaks that drip onto the harness.
A shorted switch button can pull the module's input line down and take the whole module offline, so test individual switches for continuity before replacing the module.

Can I keep driving with U01B9?

The vehicle is generally safe to drive because the fault affects accessory switches rather than engine or brake control, but avoid relying on the affected switches and have the fault diagnosed soon to prevent a more widespread network failure.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.