A faulty Switch Input Module B that has failed internally and stopped transmitting on the bus.; Damaged or corroded wiring or connectors between the switch input module and the network bus.; A blown fuse or poor power/ground connection supplying the switch input module.; A software or configuration error in the module that prevents it from communicating properly.; A fault in another module on the same network that disrupts communication (e.g., a shorted bus line).; Water intrusion or physical damage to the module or its harness, often from spills or environmental exposure.; A low battery or charging system issue that causes modules to drop offline intermittently.

DTC codes / U01xx · Lost communication with a control module / U01B8

U01B8Lost Communication With Switch Input Module B

Q: What does code U01B8 mean?

Lost Communication With Switch Input Module B. U01B8 is a generic communication fault indicating that a control module on the vehicle's network has lost contact with the Switch Input Module B, a device that reads switch states such as steering wheel or console buttons. The computer detects this when the module stops receiving the periodic status messages that the switch input module is programmed to broadcast over the communication bus.

U01B8 is a generic communication fault indicating that a control module on the vehicle's network has lost contact with the Switch Input Module B, a device that reads switch states such as steering wheel or console buttons. The computer detects this when the module stops receiving the periodic status messages that the switch input module is programmed to broadcast over the communication bus.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaLost communication with a control module

Symptoms you may notice

The check engine light or a communication warning light illuminates on the dashboard.
Often no symptoms besides the warning light, especially if the affected switches are not used frequently.
Some buttons or switches on the steering wheel or center console stop working or respond intermittently.
A related system such as cruise control, audio controls, or driver information display may become inoperative.
In rare cases, the vehicle may enter a reduced-power or limp mode if the missing module is part of a safety-critical network.
Intermittent operation of the affected switches, sometimes working again after the vehicle is restarted.

Common causes, most likely first

A faulty Switch Input Module B that has failed internally and stopped transmitting on the bus.
Damaged or corroded wiring or connectors between the switch input module and the network bus.
A blown fuse or poor power/ground connection supplying the switch input module.
A software or configuration error in the module that prevents it from communicating properly.
A fault in another module on the same network that disrupts communication (e.g., a shorted bus line).
Water intrusion or physical damage to the module or its harness, often from spills or environmental exposure.
A low battery or charging system issue that causes modules to drop offline intermittently.

How to diagnose and fix it

Verify the code with a scan tool and check for related communication codes in other modules to confirm the fault is specific to Switch Input Module B.
Inspect the wiring and connectors at the switch input module for corrosion, looseness, or damage, and repair as needed.
Check the fuse and power/ground circuits at the module using a multimeter or test light.
Perform a battery and charging system test to rule out low voltage as the root cause.
If the module is accessible, substitute it with a known-good unit of the same part number to see if communication returns.
Reprogram or reconfigure the module with the latest software if a communication glitch is suspected.
Replace the switch input module if all other checks pass and communication is still lost, then clear codes and verify the repair.

Before you replace the switch input module

A loose or corroded ground connection at the module can mimic a failed module, so always check grounds before condemning the part.
The code can be set by a completely different module on the same bus that is shorting the communication lines, so a full network scan is essential.
Some vehicles require the new module to be programmed or configured to the vehicle, and a used module may not work without proper initialization.
Intermittent communication loss is often caused by a chafed wire in a door jamb or steering column where the harness flexes, not by the module itself.
A weak battery can cause multiple modules to drop offline and set communication codes; always load-test the battery before deep diagnosis.

Can I keep driving with U01B8?

The vehicle is generally safe to drive if the only symptom is a warning light and the affected switches are non-essential, but avoid relying on systems like cruise control or steering wheel controls until the fault is repaired. If the vehicle enters limp mode or multiple warning lights appear, stop driving and have it towed to a repair facility.

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.