Damaged, corroded or disconnected wiring or connector at the transfer case control module; Blown fuse or poor ground supplying power to the transfer case control module; Failed transfer case control module, often due to water intrusion or internal circuit failure; Open or shorted CAN bus wiring between the transfer case module and the network gateway; Low battery voltage or a weak battery causing the module to drop offline intermittently; Corrosion or loose pins in the harness connector behind the transfer case or under the vehicle; A network communication fault elsewhere on the same bus segment that disrupts messages

DTC codes / U01xx · Lost communication with a control module / U0102

U0102Lost Communication with Transfer Case Control Module

Q: What does code U0102 mean?

Lost Communication with Transfer Case Control Module. U0102 means the engine or body computer has lost the controller area network (CAN) communication link with the transfer case control module, so it can no longer command four-wheel-drive or all-wheel-drive engagement. The computer sets this code when it expects regular status messages from the transfer case module and receives none within a defined time window.

U0102 means the engine or body computer has lost the controller area network (CAN) communication link with the transfer case control module, so it can no longer command four-wheel-drive or all-wheel-drive engagement. The computer sets this code when it expects regular status messages from the transfer case module and receives none within a defined time window.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaLost communication with a control module

Symptoms you may notice

Four-wheel-drive or all-wheel-drive system becomes inoperative, with the selector switch producing no response
A four-wheel-drive or service four-wheel-drive warning light illuminated on the dashboard
The transfer case may remain stuck in its last engaged mode or default to two-wheel drive
Often no symptoms besides the warning light, especially if the vehicle is driven in two-wheel drive
Multiple unrelated warning lights or communication codes appearing if the module shares a bus segment
No unusual noises or driving feel changes when the transfer case is not needed

Common causes, most likely first

Damaged, corroded or disconnected wiring or connector at the transfer case control module
Blown fuse or poor ground supplying power to the transfer case control module
Failed transfer case control module, often due to water intrusion or internal circuit failure
Open or shorted CAN bus wiring between the transfer case module and the network gateway
Low battery voltage or a weak battery causing the module to drop offline intermittently
Corrosion or loose pins in the harness connector behind the transfer case or under the vehicle
A network communication fault elsewhere on the same bus segment that disrupts messages

How to diagnose and fix it

Scan all modules for communication codes and record which modules are online to confirm the transfer case module is truly offline
Check battery voltage and perform a voltage drop test on the module's power and ground circuits
Inspect the transfer case control module connector and harness for corrosion, chafing, water intrusion or loose pins
Measure CAN bus resistance and voltage at the module connector to verify bus integrity
Check for continuity and shorts on the CAN high and CAN low wires between the module and the network gateway
Substitute a known-good transfer case control module or perform a module relearn if communication returns
Clear codes and verify communication persists through a full drive cycle before returning the vehicle

Why the transfer case module goes silent

A transfer case control module that loses power or ground will set U0102 even though the module itself is healthy, so always verify power and ground before condemning the module.
Water intrusion into the transfer case module connector is a common hidden cause on vehicles that see road spray or off-road use, and the corrosion often sits behind the pins where a visual check misses it.
U0102 can be a secondary code caused by a low or failing battery, especially if other modules also log communication codes at the same time.
The transfer case module may still respond to a scan tool on a different bus segment while the CAN link to the engine computer is broken, so a module that answers does not rule out this code.
A failed transfer case motor or encoder can draw excessive current and shut down the module's communication, making U0102 appear as a wiring fault when the actuator is the real problem.

Can I keep driving with U0102?

The vehicle usually remains safe to drive in two-wheel drive, but avoid relying on four-wheel-drive or all-wheel-drive until the fault is repaired. If the transfer case is stuck engaged or the vehicle handles unpredictably, stop driving and have it towed.

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.