Code U0003 on the 2023 Infiniti Q50 indicates that the CAN Bus A circuit is reading low - the voltage on the CAN lines is below normal operating range. This prevents proper communication between modules on the high-speed CAN network.
CAN Bus Low Condition
A 'circuit low' condition means the CAN-H and/or CAN-L lines are being pulled toward ground when they shouldn't be. This can result from a short to ground in the wiring, a module with a faulty CAN transceiver shorting the lines, or termination resistor problems that affect voltage levels.
System-Wide Effects
With U0003 active, the CAN network cannot function properly. Multiple modules report communication faults, and warning lights illuminate across the dashboard. The vehicle may start and run but with severely limited functionality, or it may not start at all if critical modules cannot communicate.
Diagnostic Methodology
Check for shorts to ground in the CAN wiring. Pinched wires under seats, damaged harnesses in door jambs, and rubbed-through insulation near sharp metal edges are common causes. A module with an internally shorted CAN transceiver can also pull the bus low. Systematic disconnection of modules helps identify the culprit.
Repair Process
Measure CAN bus voltage to confirm the low condition. Disconnect modules systematically while monitoring voltage - when voltage returns to normal, you've found the problem area. Repair wiring damage or replace the faulty module. Verify all communication is restored after repairs.