U01B7: Lost Communication With Switch Input Module A

What it means

Communication with Switch Input Module A was not received as expected. The code does not specify which switches the module serves.

At a glance

• Usually lights the warning light of the system that lost communication

How it works

Switch Input Module A collects switch signals and sends them to other vehicle controllers. This code sets when expected messages from module A are missing; it does not identify which switches that module serves.

Common causes

Most likely first.

1. Module unpowered
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules and record freeze-frame data to determine whether the communication fault is isolated to module A.
2. Check which functions are unavailable and whether Switch Input Module A responds to a scan tool.
3. Inspect module A's connectors and wiring for looseness, corrosion, damage, or water entry.
4. Check the module's power and ground circuits under load against the manufacturer's specification.
5. If its supplies are correct, test network continuity and gateway routing before replacing the module.

Common fixes

• Reconnect or repair a loose or corroded module A connector.
• Repair damaged wiring or restore module A's power and ground.
• Repair a confirmed network or gateway routing fault.
• Replace Switch Input Module A if it remains offline with verified power, ground, and communication wiring.

Can I keep driving?

Driving may be possible if essential controls still work, but functions served by Switch Input Module A can be unavailable or behave unpredictably. Avoid driving if the affected controls include safety-related functions, and have the fault diagnosed promptly.