U0102

Code

Generic U — Network/User

Lost Communication With Transfer Case Control Module

Brand: Generic

Type: U — Network/User

Views: UK: 39 EN: 53 RU: 67

AI status

Completed

ready

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Page language: EN

Causes

Open, shorted or corroded wiring between TCCM and vehicle CAN bus
Poor or missing power or ground to the Transfer Case Control Module
Blown fuse or faulty relay feeding the TCCM
Failed Transfer Case Control Module
Faulty CAN bus termination or short to battery/ground
Low battery voltage or intermittent supply

Symptoms

Malfunction Indicator Lamp (MIL) or warning lights illuminated
4WD/AWD system disabled or stuck in one mode
Transfer case will not shift between modes or engage
Dash message: 'Service 4WD', 'Transfer Case Fault', or similar
Related systems (traction control, stability, cruise) affected or derated
No data/parameters for transfer case available on a scan tool

What to check

Connect a capable scan tool: confirm U0102 and note freeze frame/related codes
Check battery voltage (key on): should be within normal range (approx. 12–14.5 V)
Inspect fuses/relays for transfer case module and CAN gateway
Visually inspect TCCM connector and wiring for damage, corrosion, or moisture
Verify other modules on same CAN network are communicating
Backprobe TCCM power and ground pins for proper voltage and solid ground

Signal parameters

CAN bus idle (recessive): CANH ≈ 2.5 V, CANL ≈ 2.5 V (common mode)
CAN bus dominant: CANH ≈ 3.5 V, CANL ≈ 1.5 V (differential ≈ 2.0 V)
Termination resistance: ≈ 60 ohms measured across CANH and CANL at a network point
Expected presence of activity: periodic CAN messages; message frequency depends on manufacturer/module (tool should show transfer case data when healthy)
Power supply to TCCM: switched 12 V when key ON (verify per vehicle wiring diagram)
Ground: low resistance to chassis (near 0 ohms)

Diagnostic algorithm

Retrieve and record all codes and freeze-frame data. Note related U-codes and module responses.
Check battery state of charge and connections. Low voltage can cause CAN faults—charge or load-test battery if suspect.
Inspect fuses and relays for the transfer case module and replace as needed.
Visually inspect TCCM connector, pins and wiring for corrosion, bent pins, water intrusion, or damage. Repair connector issues before further testing.
Using a DVOM, check for proper key-on power and a good ground at the TCCM power/ground pins.
With ignition ON, backprobe CANH and CANL at the TCCM. Verify idle voltages and look for activity with a scope or scan tool. If voltages are clamped or one line is shorted, trace wiring for short to battery or ground.
Measure termination resistance (≈60 ohms). If open or very low, locate missing or incorrect terminators or short.
Disconnect the TCCM and check if other modules regain communication (helps isolate whether the module is loading the bus).
Perform a wiggle test of the harness while monitoring CAN activity to reproduce intermittent faults.
If wiring and power/ground are good but communication is absent, consider bench/vehicle module replacement or reflash per manufacturer procedures. Reprogram TCCM if required after replacement.
Clear codes, perform a function test and road test while monitoring live data to confirm the fault is resolved.

Likely causes

Disconnected or corroded connector at the TCCM
Blown fuse or defective power/ignition relay to the TCCM
Open/short in CANH or CANL between module and gateway/PCM
Poor ground at TCCM chassis or module ground point
Failed TCCM hardware or internal CAN transceiver

Fault status

⚠️ Status

Lost Communication With Transfer Case Control Module — the vehicle network is not receiving expected messages from the TCCM. This may disable transfer case operation and related systems. Investigation should start with power/ground, fuses, connectors and CAN bus integrity before considering module replacement.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-4.0 hours