TORQDEX // POWERTRAIN DTC
Lost Communication With Anti-Lock Brake System Control Module
One or more vehicle modules have lost communication with the anti-lock brake system control module.
00 // CODE DEFINITION
What U0121 means
U0121 indicates that other modules cannot communicate normally with the ABS control module.
ABS-module power or ground loss, network wiring faults, connector problems, or an offline control module may be responsible.
01 // COMMON SYMPTOMS
What you may notice
02 // COMMON CAUSES
What can trigger U0121?
ABS module power or ground fault
Loss of module power or ground can disable communication.
CAN wiring fault
Open, shorted, or damaged network wiring can isolate the ABS module.
ABS control-module fault
An internal module problem can prevent network communication.
03 // DRIVEABILITY
Can I keep driving with U0121?
Use caution. A high-severity fault can affect engine, transmission, electrical, or emissions-system operation. If the vehicle is running poorly, overheating, losing oil pressure, flashing the check-engine light, or entering reduced-power mode, avoid continued driving until the cause is diagnosed.
04 // DIAGNOSTIC ORDER
Start here
Attempt ABS module communication
Determine whether the module is offline while other modules remain available.
Check ABS power and grounds
Verify fuses, feeds, connections, and grounds at the module.
Inspect network wiring
Check CAN wiring and connectors serving the ABS module.
Check other communication codes
Determine whether the problem is isolated to the ABS module or affects the larger network.
05 // COMMON REPAIR AREAS
Systems commonly involved
These are common areas associated with U0121. Testing should confirm the actual fault before parts are replaced.
ABS module power or ground fault
Loss of module power or ground can disable communication.
CAN wiring fault
Open, shorted, or damaged network wiring can isolate the ABS module.
ABS control-module fault
An internal module problem can prevent network communication.
06 // DIAGNOSTIC PRINCIPLE
Confirm the fault before replacing parts
U0121 identifies a condition detected by the vehicle control system. It does not automatically identify one failed component. Test the affected system before replacing parts.
07 // RELATED TORQDEX DIAGNOSTICS
Related diagnostic guides
Continue troubleshooting by symptom and system. These TorqDex guides cover common diagnostic paths associated with this trouble code.
08 // RELATED CODES