Damaged, corroded, or disconnected wiring or connector at the chassis control module; Faulty chassis control module power or ground circuit, including blown fuse or poor ground connection; Internal failure of the chassis control module itself; Controller area network bus wiring fault such as an open, short, or excessive resistance on the CAN high or CAN low line; Low battery voltage or charging system issue causing modules to drop offline intermittently; Aftermarket accessories improperly tapped into the CAN bus or chassis module wiring

DTC codes / U01xx · Lost communication with a control module / U012A

U012ALost Communication With Chassis Control Module A

Q: What does code U012A mean?

Lost Communication With Chassis Control Module A. U012A is a generic network communication code indicating that the engine control module or another primary module has lost contact with the chassis control module A over the vehicle's controller area network bus. The computer has detected that expected periodic messages from the chassis control module have stopped arriving within the required time window, which sets the code and typically illuminates the warning light.

U012A is a generic network communication code indicating that the engine control module or another primary module has lost contact with the chassis control module A over the vehicle's controller area network bus. The computer has detected that expected periodic messages from the chassis control module have stopped arriving within the required time window, which sets the code and typically illuminates the warning light.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaLost communication with a control module

Symptoms you may notice

Illumination of the antilock brake system (ABS), traction control, or stability control warning light on the dashboard
Often no symptoms besides the warning light, with the vehicle driving normally
Disabled or erratic operation of stability control, traction control, or hill descent features
Intermittent or permanent loss of communication with scan tools when trying to access the chassis control module
Other modules may store unrelated communication codes or show a 'U' code family pattern

Common causes, most likely first

Damaged, corroded, or disconnected wiring or connector at the chassis control module
Faulty chassis control module power or ground circuit, including blown fuse or poor ground connection
Internal failure of the chassis control module itself
Controller area network bus wiring fault such as an open, short, or excessive resistance on the CAN high or CAN low line
Low battery voltage or charging system issue causing modules to drop offline intermittently
Aftermarket accessories improperly tapped into the CAN bus or chassis module wiring

How to diagnose and fix it

Verify battery voltage and charging system output, as low voltage is a common cause of intermittent communication loss
Inspect the chassis control module connectors and wiring for corrosion, damage, or loose pins, and check the module's power and ground circuits
Use a scan tool to check for communication with the chassis control module and perform a network integrity test if supported
Measure CAN bus resistance and voltage levels at the diagnostic link connector to identify bus faults
Check for technical service bulletins or software updates for the chassis control module that address communication issues
If wiring and power are confirmed good, substitute a known-good chassis control module or perform module reprogramming as directed by the manufacturer
Clear codes and road test to confirm the repair, then verify no communication codes return

Chassis module communication loss traps to avoid

A loose or corroded ground connection at the chassis control module is a frequent culprit that many technicians overlook when focusing on the CAN bus wiring itself.
This code does not always mean the chassis control module has failed; a simple blown fuse or low battery voltage can set U012A intermittently and clear once voltage is restored.
Aftermarket alarms, remote starters, or dash cameras tapped into the CAN bus can disrupt communication and set U012A without any factory component being faulty.
Some vehicles require the chassis control module to be initialized or programmed after replacement, and skipping this step will cause the code to return immediately.
U012A can be stored alongside other U codes when a single bus fault affects multiple modules, so always diagnose the root network issue rather than replacing modules one by one.

Can I keep driving with U012A?

The vehicle is generally safe to drive if only the warning light is on and brakes feel normal, but avoid relying on stability control or traction control features until the fault is repaired. If the ABS or brake warning light is also illuminated, have the system inspected promptly because braking assist features may be compromised.

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.