U0102Generic code

U0102 Code: Lost Communication with Transfer Case Control Module

The U0102 code means other modules in the vehicle stopped receiving messages from the transfer case control module. The usual effect is that four wheel drive does not engage or does not disengage. You can generally keep driving, but the functions of that module may not be available.

Severity
Medium
Can I keep driving?
Yes, no immediate risk
Estimated cost
$0 to $1,500
Difficulty
Medium
System
Communication Network
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the U0102 code means

The modules in the vehicle exchange information constantly over the data network, normally CAN. The transfer case control module controls the switch between 2WD and 4WD and the torque split. When the other modules stop receiving its messages for a while, they log the U0102 code.

The code is stored by the module that misses the information, not by the one that is failing. That is why it often shows up in several modules at once. The problem can be in the transfer case control module itself (no power, no ground or failed), in its connector or in the network wiring that reaches it.

Usual location: near the transfer case or under the dash. If that area is exposed to water or was recently repaired, start there.

Work the diagnosis in this order: 1) battery and alternator, because low system voltage is the number one cause of bursts of U codes; 2) the module list on the scan tool, to see which module is not responding; 3) power, fuses and grounds of the module that is not responding; 4) network resistance at the OBD2 connector, about 60 ohms between pins 6 and 14 with the battery disconnected; 5) connectors and wiring at the module, especially in areas exposed to moisture such as under the carpets, in the doors and in the trunk.

Measuring the network and isolating the module that is bringing it down is the heart of any U code diagnosis, so take the time to do those steps in order before you replace anything.

U0102 code symptoms

  • Warning lights on the dash.
  • Four wheel drive does not engage or does not disengage.
  • Communication codes in several modules at the same time.
  • The fault can be intermittent, for example in the rain or over bumps.

Likely causes of the U0102 code

  1. Module power or ground: a blown fuse, a corroded ground or a loose power connector.
  2. Weak battery or low voltage: it makes modules reboot and lose communication.
  3. Module connector with water or corrosion: very common for modules located in wet areas.
  4. Damaged network wiring: CAN high or CAN low cut or shorted.
  5. Failed transfer case control module: only after ruling out everything above.
  6. Poorly installed accessory: alarms or trackers wired into the network.

How to diagnose the U0102 code step by step

  1. Measure the battery voltage at rest (12.4 to 12.7 V) and with the engine running (13.5 to 14.7 V).
  2. Check on the scan tool which modules respond. If the transfer case control module does not show up, the fault is in the module or in its connection.
  3. Check the module fuses and grounds using the wiring diagram.
  4. Measure the network at the OBD2 connector. You should see about 60 ohms between pins 6 and 14 with the battery disconnected, and roughly 2.5 V on each wire with the key on.
  5. Inspect the module connector for moisture, corrosion and bent pins.
  6. Measure CAN high and CAN low at the module connector. They should have continuity with the OBD2 connector.

How to fix the U0102 code

  • Repair the module power, ground or connector.
  • Repair the network wiring.
  • Replace and program the module if it has failed, which almost always requires programming.
  • Clear the codes in all modules and verify.

Technical reference data

  • CAN network resistance between OBD2 pins 6 and 14: about 60 ohms.
  • CAN high: 2.5 to 3.5 V. CAN low: 1.5 to 2.5 V.
  • These values are a guide only, so check the manufacturer data for your vehicle.

Brand-specific notes

After you fix the U0102 code, clear the codes in all modules. Many of them keep old U codes from the time the fault was present. Accessories installed after the sale, such as alarms, GPS trackers and OBD2 adapters left plugged in permanently, are a frequent cause of network problems.

Frequently asked questions about U0102

Can I drive with a U0102 code?
Yes, in general. The functions of that module, such as four wheel drive, may not be available.
Does U0102 mean the transfer case control module is bad?
Not necessarily. The most frequent cause is its power, its ground, its connector or the battery.
Why do so many codes show up at once?
Because every module that was waiting for information from the affected module logs the fault.
How much does it cost to fix U0102?
Between $0, if it was the battery or a fuse, and $1,500 if the module has to be replaced and programmed.
What does the U0102 code mean?
It is a generic OBD2 code that means other modules lost communication with the transfer case control module. The code does not say which part of the circuit has the fault.
Will a U0102 code clear itself?
Only if the cause was temporary, such as a low battery that was recharged. If a connector, a ground or the module is at fault, the code comes back.
What is the most common cause of U0102?
Power or ground problems at the module, a weak battery or a connector with water or corrosion. A failed module is the last thing to suspect.

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