Fault Family System: Network (U-Codes) 32 SAE Codes

Lost Comm Chassis ABS Module

Diagnostic & Technical Explanation

U0121 indicates loss of contact with a chassis-dynamics module -- ABS/stability control, steering angle sensor, ride-height/suspension control, power steering, or a differential/brake-blending actuator -- all mounted low near the subframe, wheel wells, or under-floor tunnel where connectors take the worst exposure to road salt, water spray, and vibration of any module class. Unlike cabin electronics, these connectors are often sealed but still fail at the seal itself after years of thermal cycling, so a corroded or water-intruded low-mount connector is the dominant cause ahead of any harness break.

These 32 diagnostic trouble codes share one detection mechanism and one repair path, which is why MechanicDB groups them into a single authored fault family rather than repeating the same explanation 32 times.

Codes in this family (32)

Code	Definition	Repair coverage
U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module A	4 ranked fixes
U0122	Lost Communication With Vehicle Dynamics Control Module	4 ranked fixes
U0123	Lost Communication With Yaw Rate Sensor Module	4 ranked fixes
U0124	Lost Communication With Lateral Acceleration Sensor Module	4 ranked fixes
U0125	Lost Communication With Multi-axis Acceleration Sensor Module A	4 ranked fixes
U0126	Lost Communication With Steering Angle Sensor Module	4 ranked fixes
U0127	Lost Communication With Tire Pressure Monitor Module	4 ranked fixes
U0128	Lost Communication With Park Brake Control Module	4 ranked fixes
U0129	Lost Communication With Brake System Control Module A	4 ranked fixes
U012A	Lost Communication With Chassis Control Module A	4 ranked fixes
U012B	Lost Communication With Chassis Control Module B	4 ranked fixes
U012C	Lost Communication With Active Vibration Control Module	4 ranked fixes
U0130	Lost Communication With Steering Effort Control Module	4 ranked fixes
U0131	Lost Communication With Power Steering Control Module A	4 ranked fixes
U0132	Lost Communication With Suspension Control Module A	4 ranked fixes
U0133	Lost Communication With Active Roll Control Module	4 ranked fixes
U0134	Lost Communication With Power Steering Control Module - Rear	4 ranked fixes
U0135	Lost Communication With Differential Control Module - Front	4 ranked fixes
U0136	Lost Communication With Differential Control Module - Rear	4 ranked fixes
U0137	Lost Communication With Trailer Brake Control Module	4 ranked fixes
U0138	Lost Communication With All Terrain Control Module	4 ranked fixes
U0139	Lost Communication With Suspension Control Module B	4 ranked fixes
U014E	Lost Communication With Multi-axis Acceleration Sensor Module B	4 ranked fixes
U015A	Lost Communication With Anti-Lock Brake System (ABS) Control Module B	4 ranked fixes
U015B	Lost Communication With Power Steering Control Module 'B'	4 ranked fixes
U01B3	Lost Communication With Brake Blending Actuator	4 ranked fixes
U01B4	Lost Communication With Brake System Control Module B	4 ranked fixes
U01BA	Lost Communication With Park Lock/Pawl Control Module	4 ranked fixes
U025E	Lost Communication With Electronic Brake Booster Control Module A	4 ranked fixes
U025F	Lost Communication With Electronic Brake Booster Control Module B	4 ranked fixes
U02A6	Lost Communication With Safety Integration Control Module	4 ranked fixes
U064D	Lost Communication With Trailer Brake Control Switch	4 ranked fixes

What this page does not show

This page publishes the fault mechanism and the code index. The licensed dataset adds, for every one of the 15,886 codes, the full authored repair set (56,729 procedures in total) with the fields deliberately withheld here:

Procedures 2..n after the first-listed procedure
Aftermarket parts cost ranges in USD (est_parts_cost_min/max_usd)
Professional labor-hour estimates (est_labor_hours)
Step-by-step diagnostic and repair instructions
Replacement-part mappings and catalog lookups
6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)

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