Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.
There is a service bulletin for the 2003 Nissan Altima:
2003 Nissan Altima Factory Service Bulletin OBDII Code U1000
Usually, the problem is poor harness ground connection. The service bulletin suggests cleaning engine and body harness ground connection to repair the problem. Loosen the ground connectors clean them with sandpaper on the connector side and body side and retighten the bolts back.
The cost to diagnose the U1000 2003 NISSAN ALTIMA SEDAN code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.
The Controller Area Network (CAN) is a serial communication line for real-time applications. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN H line, CAN L line) allowing a high rate of information transmission with less wiring.
Each control unit transmits/receives data but selectively reads the required data only.
The Diagnostic Trouble Code (DTC) sets when the Engine Control Module (ECM) is not transmitting or receiving CAN communication signals of OBD (emission-related diagnosis) for 2 seconds or more.
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