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Network Codes (U-Codes): Full List

Network codes start with U and mean that control modules have stopped talking to each other properly over the vehicle's data network, usually the CAN bus. A U code rarely points to a failed part on its own: weak battery voltage, a poor ground, corroded or loose connectors and water intrusion are common causes. Several U codes at once often share one root cause, so read them all before replacing anything.

42Codes
3.1Average severity
33%High or critical
5%DIY-friendly
Severity distributionSeverity distribution

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U0105 Network The PCM lost contact with the separate module that fires the injectors, common on diesel… High U0101 Network The engine computer and other modules stopped hearing from the transmission control module. High U0121 Network Other modules stopped receiving data from the ABS module, so ABS and stability control are off. Moderate U0001 Network A module found the high-speed CAN network itself misbehaving, not just one silent module. High U0122 Network Other modules lost contact with the stability control computer, so ESC and traction control… Moderate U0418 Network Brake-control data such as pedal position or brake-assist status looks implausible to another… High

All codes (32)

All Severity 3+ Severity 4+
U1064 Chevrolet · Network Other modules stopped hearing the body control module on an older GM's Class 2 data line. Moderate U1900 Ford · Network A Ford module stopped receiving messages it expects from another module on the CAN network. Moderate

Subsystems

Module Communication 43

Systems

Powertrain 539Chassis 37Body 30