U0102: Lost Communication with Transfer Case Control Module

What it means

A control module has lost communication with the transfer case control module. Four-wheel-drive functions may be affected, depending on the vehicle and which module reported the code.

How it works

The transfer case control module manages four-wheel-drive functions such as selecting or monitoring transfer case modes on vehicles equipped with it. Other modules exchange status and commands with it over the vehicle network. U0102 sets when a reporting module stops receiving expected messages from the transfer case module.

Common causes

Most likely first.

1. Loss of transfer case module power or ground
2. Open, shorted, or damaged communication wiring or connector
3. Module or gateway fault

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 note which ones report U0102, other communication codes, and freeze-frame conditions to see whether the fault is isolated or network-wide.
2. Check whether the four-wheel-drive controls and transfer case status are available, and record any warning messages or mode changes.
3. Inspect the transfer case module connectors and nearby harness for loose plugs, corrosion, water intrusion, chafing, or impact damage.
4. Check the module's power and ground circuits under the conditions in which the fault occurs, comparing results with the manufacturer's specification.
5. Test the communication wiring between the transfer case module and the network for opens, shorts, or poor connections using the vehicle wiring information.
6. If power, ground, and network wiring are sound, check for gateway or transfer case module faults with vehicle-specific diagnostic information before replacing a module.

Common fixes

• Repair a loose or corroded transfer case module connector.
• Repair damaged network wiring or a poor ground connection at the module.
• Restore module power by repairing its supply circuit or replacing a failed fuse after checking for the cause.
• Repair a network gateway fault if testing identifies it.
• Replace or program the transfer case control module only after its power, ground, and communication circuits pass testing.

Can I keep driving?

If the vehicle drives normally, a short, cautious trip may be possible, but four-wheel-drive modes may be unavailable or unreliable. Avoid relying on four-wheel drive in poor traction, and stop if shifting, driveline behavior, or other warnings indicate a safety problem.