Home›Trouble Codes›U0102

U0102 — Lost Communication Transfer Case Control Module

Generic OBD-II · all makesNetwork / communication

U0102 indicates that the vehicle's powertrain control module (PCM) has lost communication with the Transfer Case Control Module (TCCM) over the CAN bus. This prevents the PCM from receiving status or sending commands to the transfer case, which can affect 4WD operation.

Symptoms

What causes it — most likely first

1. Damaged wiring or corroded connectors

The harness or pins linking the TCCM to the CAN bus can suffer from chafing, moisture intrusion, or corrosion, interrupting communication.

2. Faulty Transfer Case Control Module

Internal failure of the TCCM (e.g., microprocessor or transceiver fault) can prevent it transmitting or receiving messages on the bus.

3. Power supply or ground issue to the TCCM

A blown fuse, faulty relay, poor ground strap, or insufficient voltage can cause the module to reset or lose communication.

4. CAN bus communication fault

A short to voltage, open circuit, or excessive noise on the CAN high/low lines (often caused by another module or wiring fault) can block TCCM messages.

5. Software glitch requiring re-flash

Corrupted or outdated firmware in the TCCM may cause it to stop responding until the module is reprogrammed.

6. PCM/ECM failure (rare)

While the PCM could theoretically fail to transmit/receive CAN messages, this is uncommon; other causes should be exhausted first.

How it's diagnosed

  1. Scan for all stored and pending codes, noting any related CAN or module communication codes that may point to a bus issue.
  2. Visually inspect the TCCM connector and wiring harness for damage, corrosion, loose pins, or water intrusion; repair as needed.
  3. Measure voltage at the TCCM power feed and check ground continuity with a multimeter; verify proper supply and ground per service specifications.
  4. Use a scan tool or oscilloscope to monitor CAN high and low signals while attempting to communicate with the TCCM; look for proper voltage swings and absence of bus faults.
  5. If wiring, power, ground, and bus are good, attempt to read data from the TCCM via the scan tool; lack of response indicates a likely module failure.
  6. If the module responds but the code persists, check for available TCCM software updates or perform a re-flash; if still unsuccessful, consider PCM/ECM evaluation as a last resort.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0100 — Lost Communication EcmpcmU0101 — Lost Communication TcmU0103 — Lost Communication Gear Shift Control U0104 — Lost Communication Cruise Control ModuU0105 — Lost Communication Fuel Injector ContrU0106 — Lost Communication Glow Plug Control M

Frequently asked

Do I need to replace the PCM/ECM to fix U0102?

No. PCM/ECM failure is a very rare cause of U0102. Most cases are due to wiring, connector, power/ground issues, or the transfer case control module itself. Replace the PCM only after all other possibilities have been ruled out.

Can a blown fuse cause this code?

Yes. If the fuse supplying power to the TCCM is open, the module will lose power and cannot communicate, triggering U0102.

Is it safe to drive with U0102 active?

Driving is possible but the transfer case may remain in 2WD mode, disabling 4WD capability. This can affect traction in slippery conditions, so repair is recommended before relying on 4WD.

Will clearing the code fix the problem?

Clearing the code only turns off the warning light; if the underlying communication fault remains, the code will return shortly after driving.