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U0121 U0xxx · 网络通信（U） 高严重度
Lost Communication with ABS / ESP Control Module
The ABS module has dropped off the bus. Stability and traction functions are gone, and other modules usually complain too.
严重程度说明： 高——立即停车诊断，继续行驶有扩大损坏的风险
你会注意到的故障现象
- ABS and ESP lamps on
- ABS module unreachable
- Steering angle and yaw codes alongside
常见原因
按可能性从高到低排列——从最上面开始查。
- 1 ABS module power or earth fault
- 2 Corroded connector at the modulator
- 3 CAN wiring fault
- 4 Failed module
如何排查
先做花钱最少、侵入最小的检查——大多数这类码不是零件问题。
- ✓ Check the ABS fuses and the high-current supply first.
- ✓ Inspect the modulator connector for corrosion or water.
- ✓ Measure CAN at the ABS connector.
- ✓ Isolate the module to confirm it is not dragging the bus.
维修方案
- Repair the supply or earth
- Repair the CAN wiring
- Replace the module if failed
U0121 —— 常见问题
Do the brakes still work? +
Base braking remains. You lose ABS and stability intervention — urgent but not immobile.
Why do steering angle codes appear too? +
Other modules depend on data the ABS module normally relays.