A weak or failing 12-volt battery or poor charging system voltage causing modules to drop offline; Corroded, loose, or backed-out terminals in the connectors at the planetary gear set control module; Damaged, chafed, or open wiring in the CAN bus or power/ground circuits serving that module; Water intrusion into the module connector or housing, common at underbody or transmission-mounted locations; A failed planetary gear set control module itself, either internally or due to a faulty internal CAN transceiver; A network fault elsewhere on the bus, such as a shorted CAN line or another module holding the bus down; Improper voltage supply or ground at the module caused by a blown fuse or corroded ground point

DTC codes / U01xx · Lost communication with a control module / U01B2

U01B2Lost Communication With Planetary Gear Set Control Module

Q: What does code U01B2 mean?

Lost Communication With Planetary Gear Set Control Module. U01B2 is a generic communication fault indicating that one control module on the vehicle's network has stopped receiving messages from the planetary gear set control module, which manages the clutches and brakes inside the transmission's planetary gearset. The detecting module sets this code when the expected controller area network (CAN) messages from that module fail to arrive for a calibrated period, not when the gear set itself has a mechanical failure.

U01B2 is a generic communication fault indicating that one control module on the vehicle's network has stopped receiving messages from the planetary gear set control module, which manages the clutches and brakes inside the transmission's planetary gearset. The detecting module sets this code when the expected controller area network (CAN) messages from that module fail to arrive for a calibrated period, not when the gear set itself has a mechanical failure.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaLost communication with a control module

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) or a transmission warning message on the dash
Often no symptoms besides the warning light, with the vehicle driving and shifting normally
Harsh or delayed shifts, or the transmission stuck in a single limp-home gear
Failure to engage drive or reverse, or a neutral condition after selecting a gear
Other unrelated warning lights or module communication codes appearing at the same time
Intermittent symptoms that appear in damp weather or over rough roads

Common causes, most likely first

A weak or failing 12-volt battery or poor charging system voltage causing modules to drop offline
Corroded, loose, or backed-out terminals in the connectors at the planetary gear set control module
Damaged, chafed, or open wiring in the CAN bus or power/ground circuits serving that module
Water intrusion into the module connector or housing, common at underbody or transmission-mounted locations
A failed planetary gear set control module itself, either internally or due to a faulty internal CAN transceiver
A network fault elsewhere on the bus, such as a shorted CAN line or another module holding the bus down
Improper voltage supply or ground at the module caused by a blown fuse or corroded ground point

How to diagnose and fix it

Perform a full scan of all modules and record every communication code to see which modules are offline and whether U01B2 is the only code
Check battery state of health and charging voltage, and load-test the battery before condemning any module
Inspect and clean the connectors at the planetary gear set control module, looking for corrosion, water intrusion, and backed-out pins
Measure CAN bus resistance and voltage at the diagnostic connector to confirm the bus is intact and not shorted
Check power, ground, and wake-up signals at the module connector with a multimeter or oscilloscope while wiggling the harness
If wiring and power are good, substitute a known-good module or perform a module communication test to confirm the module is at fault
After repair, clear codes and verify communication with the module returns and no related codes reset during a road test

Communication Codes Are Rarely the Module Itself

A U01B2 is a lost-communication code, so the first suspect is the network and power supply, not the planetary gear set control module, and technicians who replace the module first often find the code returns.
Low battery voltage during cranking or a failing alternator can take a module offline long enough to set U01B2 without leaving any other symptom, so always load-test the battery before deeper diagnosis.
Water intrusion at underbody or transmission-mounted connectors is a frequent hidden cause, and the corrosion is often on the back side of the connector where a quick visual check misses it.
A shorted CAN line or a failed module elsewhere on the bus can pull the network down and produce U01B2 along with codes for several other modules, so read every module before deciding which one is faulty.
The code does not mean the planetary gear set is mechanically damaged; it only reports that the control module's messages stopped arriving, and the transmission may still shift normally once communication is restored.

Can I keep driving with U01B2?

If the vehicle drives and shifts normally, it is usually safe to drive to a repair shop, but avoid long trips and heavy towing until the fault is diagnosed. If the transmission is in limp-home mode, slipping, or refusing to engage a gear, stop driving and have the vehicle towed to prevent further damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.