CAN network

U0102 — Lost Communication with Transfer Case Control Module

Severity: medium Safe to drive

What U0102 means

U0102 means another control module, such as the engine or body controller, stopped receiving messages from the Transfer Case Control Module (TCCM) over the CAN bus. The TCCM normally manages 4WD/AWD engagement and drive mode changes. Without communication, the system can't shift reliably and often falls back to a default mode.

Symptoms

  • 4WD/AWD warning light or service message
  • Unable to switch between 2WD, 4WD and AWD
  • Drivetrain stuck in a single mode
  • Reduced traction or odd drivetrain behavior
  • Other warning lamps on at the same time
  • Additional U-codes stored

Possible causes

  1. Open, shorted or damaged CAN bus wiring
  2. Corroded or loose connectors at the TCCM or network splice points
  3. Faulty Transfer Case Control Module
  4. Poor power or ground supply to the TCCM
  5. Low system voltage from a weak battery or charging problem
  6. Software glitch or outdated module programming

How to diagnose

  1. Test battery and charging system voltage and correct any problem
  2. Run a full-system scan to see which modules aren't responding and which other U-codes are stored
  3. Inspect the TCCM harness and connector for chafing, moisture, corrosion or past repair damage
  4. Check TCCM power and ground circuits against the wiring diagram
  5. Measure CAN voltages and bus resistance at the diagnostic connector (about 60 ohms on a healthy bus)
  6. Test CAN wires for opens and shorts to ground or power
  7. If needed, unplug suspect modules one at a time, only following a documented procedure
  8. Check for available software updates for the module

Common fixes

  • Repair or replace damaged CAN wiring and connectors
  • Clean corroded terminals, secure connectors and apply dielectric grease
  • Restore proper power and ground to the TCCM
  • Replace the TCCM and program it with the correct VIN and software
  • Update or reflash the module software

Questions and answers

What does U0102 mean?

It means communication with the transfer case control module was lost on the CAN bus. Other modules no longer receive its data, so 4WD/AWD may shut down.

Can I drive with a U0102 code?

Usually yes, but without dependable 4WD/AWD. Avoid off-road driving and slippery surfaces, and have it diagnosed soon.

What should I check first for U0102?

Start with battery voltage, then the TCCM connector and wiring, its power and ground, and finally the CAN bus itself. A corroded connector or damaged wire is a common cause.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.