U0102 code meaning
Lost Communication With Transfer Case Control Module
What U0102 means
U0102 is logged when the transfer case control module, which shifts between two- and four-wheel drive and between high and low range, stops sending. GM's 2025 engine controllers expect frame $035 and fail it when gaps exceed 425 ms within a 5 s window; the code is Type C, emissions-neutral and without MIL. The earlier two-mode hybrid trucks (2012 table) used Type B with 500 ms detection between 10 and 18 V. Ford's 2023 diesel controllers allow 5 s before flagging the TCCM. Bulletin 08-07-30-021H lists U0102 among GMLAN codes caused by shared bus faults. The driver mostly sees a 4WD warning and a transfer case left in its last range; engine and gearbox keep running. U0403 covers implausible data from the same module.
U0102 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0102
- 4WD or AWD warning, range selection ignored
- Transfer case stays in its last mode
- Usually no MIL
Common causes of U0102
- Most likelyTransfer case module without power or ground
- PossibleWater or corrosion in the module connector (often mounted low on the frame)
- PossibleDamaged CAN lines to the transfer case module
- Less likelyTransfer case module internally faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transfer case control moduleCAN bus wiring
What each part of U0102 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 02 | The exact fault in that area. |
What to do next
- Note U0102 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0102
What does U0102 mean?
U0102 means "Lost Communication With Transfer Case Control Module". U0102 is logged when the transfer case control module, which shifts between two- and four-wheel drive and between high and low range, stops sending. It is a generic code, so it means the same on every make.
Is it safe to drive with U0102?
U0102 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0102 fail an emissions test?
U0102 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0102 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U0102 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.