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U0102 – Lost Communication with Transfer Case Control Module (OBD2)

U0102 means "Lost Communication with Transfer Case Control Module". A 'lost communication' code is stored by one control unit when it stops receiving the expected messages from another control unit on the data bus – here a powertrain-related module.

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U0102 quick summary

Fault codeU0102
MeaningLost Communication with Transfer Case Control Module
SystemNetwork / CAN Bus
VehiclesGeneric OBD2
SeverityHigh
Can I drive?If the engine and gearbox work normally and the code is old, carefully yes. If warning lights are on, the gearbox is in limp mode or the engine does not start, have it checked first.
Repair cost€0 – €1,000

What 'lost communication' codes mean

Control units send messages to each other on the CAN bus continuously. If one module stops hearing from another for longer than a set time, it stores a U01xx code naming the missing module – for example U0100 'lost communication with ECM/PCM' or U0101 'with TCM'.

The module named in the code is the one that has gone silent; the code itself is stored in other modules. That is why the first question is: can the scan tool still talk to the named module? If not, check its power supply, ground, fuses and bus wiring. If it can, the fault was probably temporary – for example low voltage during cranking.

Powertrain modules include the engine, transmission, fuel pump, glow plug, throttle, EGR, turbocharger, reductant (AdBlue), fuel additive and hybrid/electric drive modules. Losing communication with them often causes limp mode or a no-start.

Symptoms of U0102

  • Several warning lights on
  • Engine does not start or stalls
  • Gearbox in limp mode
  • Related functions not working
  • Code stored in several other modules

Most common causes of U0102 (most likely first)

Mechanic's Pro Tip

A single old 'lost communication' code with no symptoms is usually the result of a flat battery or jump start. Clear it and see if it comes back before starting a long diagnosis.

  1. 1.Low battery voltage or a recent battery problem

    Most likely

  2. 2.Blown fuse or missing power/ground to the named module

  3. 3.CAN wiring or connector fault

  4. 4.Water damage in the named module

  5. 5.Failed control module

Step-by-step diagnostic guide

  1. 1

    Check the battery

    Measure the battery voltage and check the terminals – many communication codes come from low voltage.

  2. 2

    Scan all modules

    Check whether the named module responds to the scan tool and which modules store the code.

  3. 3

    Check power and ground

    Check the fuses, power supply and ground of the named module.

    Multimeter: Supply near battery voltage; ground voltage drop below about 0.1 V under load.

  4. 4

    Check the bus wiring

    Check the CAN wiring and connector at the module for corrosion and damage; measure CAN resistance and voltages.

  5. 5

    Clear and retest

    Clear all codes, start the car several times and rescan. Replace the module only if it still cannot be reached with good power, ground and wiring.

Frequently asked questions

Can I keep driving with U0102?

If the engine and gearbox work normally and the code is old, carefully yes. If warning lights are on, the gearbox is in limp mode or the engine does not start, have it checked first.

How much does it cost to fix U0102?

Typical repair costs are 0 € – 1000 €, depending on the cause and the vehicle. The most common fixes are: low battery voltage or a recent battery problem; blown fuse or missing power/ground to the named module; cAN wiring or connector fault. Always confirm the cause with the tests above before buying parts.

Which module is faulty?

The code names the module that stopped communicating. The module storing the code is usually fine.

Can a weak battery cause lost communication codes?

Yes, very often – especially after cranking with low voltage or a jump start.

What is the difference between U0102 and similar codes?

U0102 belongs to a group of codes for the same component that differ in the type or location of the fault: U0100 – Lost Communication With ECM/PCM A; U0101 – Lost Communication with TCM; U0103 – Lost Communication With Gear Shift Module; U0104 – Lost Communication With Cruise Control Module; U0105 – Lost Communication With Fuel Injector Control Module; U0106 – Lost Communication With Glow Plug Control Module. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.