U0102: Lost communication with transfer case control module

What U0102 means

On four-wheel or all-wheel drive vehicles, the transfer case splits drive between the front and rear axles and has its own control unit. Another unit has stopped receiving its messages over the data network. Without it, four-wheel drive may disengage or fail to change mode.

Most common causes

• Weak battery or loose terminals
• Transfer case control unit supply fuse or relay
• That unit’s connector loose, corroded or wet (it often sits underneath)
• Damaged network wiring to the transfer case
• Failed transfer case control unit

Symptoms

• Four-wheel drive or engine warning light on
• 4x4 or low range will not engage
• Drive mode indicator flashing
• Sometimes ABS or stability control warnings too

Can you drive with U0102?

With care You can drive carefully on the road, usually in two-wheel drive. Avoid off-road, snow or mud until it is fixed, as four-wheel drive may not work.

How to check it

Find the transfer case control unit connector, often next to the transfer case underneath, and check for water or mud. Also check the four-wheel drive fuses listed in the handbook.

How to read and clear U0102 with Final OBD

Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see U0102 with this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

• U0100 Lost communication with engine control module (ECM/PCM A)
• U0101 Lost communication with transmission control module (TCM)
• U0103 Lost communication with the gear shift module
• U0104 Lost communication with the cruise control module
• U0107 Lost communication with the throttle actuator control module
• U0121 Lost communication with the ABS control module
• U0126 Lost communication with the steering angle sensor module
• U0128 Lost communication with the park brake control module
• U0131 Lost communication with the power steering control module
• U0140 Lost communication with the body control module (BCM)

U0102 is a generic code, so it means the same on any make, for example on BMW, Citroën, Ford, Mercedes-Benz, Renault, Volvo. See what Final OBD does on your car in makes and models.