Damaged or corroded trailer brake switch wiring harness, especially at the connector or where it flexes; Failed trailer brake control switch itself, internal open circuit or stuck contact; Poor ground connection for the trailer brake switch or its control module; Blown fuse or missing power feed to the trailer brake switch circuit; CAN bus wiring fault such as an open, short, or excessive resistance on the network leg serving the switch; Failed trailer brake control module or integrated body control module that hosts the switch interface; Aftermarket trailer brake controller installation that disturbed factory wiring or bus termination

DTC codes / U06xx · Network communication / U064D

U064DLost Communication With Trailer Brake Control Switch

Q: What does code U064D mean?

Lost Communication With Trailer Brake Control Switch. U064D is a generic network communication code indicating that one or more control modules on the vehicle's Controller Area Network (CAN) bus have stopped receiving messages from the trailer brake control switch. The computer detects this when the expected periodic data frame from that switch module is missing for a calibrated number of consecutive cycles, which sets the code and typically illuminates the trailer brake or stability control warning light.

U064D is a generic network communication code indicating that one or more control modules on the vehicle's Controller Area Network (CAN) bus have stopped receiving messages from the trailer brake control switch. The computer detects this when the expected periodic data frame from that switch module is missing for a calibrated number of consecutive cycles, which sets the code and typically illuminates the trailer brake or stability control warning light.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Trailer brake or stability control warning light illuminated on the dashboard
Trailer brakes may not apply or may apply erratically when towing
No trailer brake output at the connector even when the manual override is pressed
Message center displays a 'Trailer Brake System Fault' or similar warning
Often no symptoms besides the warning light when no trailer is connected
Other unrelated warning lights may appear if the fault disrupts shared bus traffic

Common causes, most likely first

Damaged or corroded trailer brake switch wiring harness, especially at the connector or where it flexes
Failed trailer brake control switch itself, internal open circuit or stuck contact
Poor ground connection for the trailer brake switch or its control module
Blown fuse or missing power feed to the trailer brake switch circuit
CAN bus wiring fault such as an open, short, or excessive resistance on the network leg serving the switch
Failed trailer brake control module or integrated body control module that hosts the switch interface
Aftermarket trailer brake controller installation that disturbed factory wiring or bus termination

How to diagnose and fix it

Inspect the trailer brake switch connector and harness for corrosion, chafing, or loose pins, and repair as needed
Check all fuses and grounds serving the trailer brake switch and its module, cleaning and tightening connections
Measure voltage and resistance on the switch signal circuit according to the factory wiring diagram to confirm power and ground integrity
Use a scan tool to monitor live data for the trailer brake switch and verify whether the switch state changes when operated
Perform a CAN bus integrity test with an oscilloscope or break-out box to rule out network wiring faults on the leg serving the switch
Substitute a known-good trailer brake switch or module only after wiring and power checks pass, then clear codes and retest
If the fault persists, follow the manufacturer's diagnostic flow for the trailer brake control module and reprogram or replace it as directed

Trailer brake switch faults that mimic network codes

A weak or intermittent ground at the trailer brake switch can drop its CAN messages without ever blowing a fuse, so voltage-drop testing under load is more reliable than a simple continuity check.
Aftermarket trailer brake controllers tapped into the factory harness are a frequent cause of U064D because they can introduce bus termination errors or back-feed voltage that corrupts communication.
The code can set intermittently when the trailer connector is left plugged in during wet weather, allowing water intrusion to short the switch signal circuit without permanent damage.
Some vehicles only power the trailer brake switch circuit when a trailer is detected, so the code may not reappear during a bench test unless the scan tool commands trailer mode or a test load is connected.
U064D is often stored alongside U0100 or U0140 when the root cause is a shared bus fault rather than the switch itself, so always check for multiple communication codes before condemning the switch.

Can I keep driving with U064D?

You can drive the vehicle without a trailer, but trailer braking will be compromised or absent, so do not tow until the fault is repaired. Avoid towing any trailer with electric brakes because the loss of communication may prevent the trailer brakes from engaging in an emergency.

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.