U025387 - U025387 Lost Communication With Compressor

Detailed Fault Definition

U025387 "Communication Lost with Compressor" is a critical network communication fault code defined within automotive electronic control systems. This code indicates that when the Vehicle Controller attempts to read from or write to the Electric Compressor module via data buses such as the Controller Area Network (CAN Bus), it fails to receive the expected response signal. In an automotive air conditioning system architecture, this code signifies a physical or logical break in the feedback loop between the master controller and the actuator, preventing the system from acquiring real-time status data, operating parameters, and fault information from the compressor in real time, which may trigger vehicle-level protective strategies for the AC system.

Common Fault Symptoms

When the U025387 fault code is stored and illuminated, vehicles typically exhibit the following perceivable dynamic characteristics or static feedback:

• The dashboard air conditioning control switch indicator light extinguishes or displays a fault alert icon.
• Interior ambient temperature regulation fails; the compressor clutch does not engage, resulting in complete or partial loss of cooling function.
• Network message loss warnings received when reading via the On-Board Diagnostics (OBD) interface.
• Potential recording of anomaly logs for other associated systems while the engine is running.

Core Fault Cause Analysis

According to technical data analysis, the trigger source of this fault code mainly focuses on hardware or logic levels in the following three dimensions:

• Hardware Component Level: Primarily involves damage to core electronic components of the Electric Compressor itself. This includes control chip failure inside the compressor, motor winding short circuit/open circuit, or the compressor module Power Management Unit (PMU) being unable to maintain a normal communication state.
• Wiring and Connector Level: Focuses on inspecting the integrity of power supply circuits and signal transmission channels. This includes fuse melting (Fuse Failure) for compressor power supply, causing the compressor to lose power or unstable voltage; additionally, insulation layer damage due to harness wear, short circuit or open circuit to ground, as well as connector pin oxidation, poor contact, or physical detachment, all lead to CAN signal transmission interruption.
• Controller Level: Involves communication protocol processing logic inside the control unit. If the controller's gateway module has abnormalities in parsing the compressor's data frames, or if its internal watchdog timer fails to receive correct heartbeat packets, a loss of communication is determined.

Technical Monitoring and Trigger Logic

The controller follows strict time sequence and numerical threshold logic for judging this fault, with specific monitoring mechanisms as follows:

• System Startup Readiness Conditions: The controller must be powered on, or detect CAN signals valid for at least $5s$ while in the ON gear (ignition on). Meanwhile, the system monitors that the vehicle battery voltage range must be stable between $9V \sim 16V$.

• Communication Monitoring Metrics: The controller continuously listens to feedback messages from the compressor. Once any monitored message is detected to be lost continuously more than $10$ times, it is judged as an effective communication interruption.

• Status Exclusion Logic: Before judging a fault, the system must confirm that the current network architecture is not in a non-normal working mode. Specifically, the bus cannot be in a BUS OFF state (referring to physical layer disconnection or protocol errors causing bus shutdown), and this fault code cannot be covered by a Muted status.

Only when all voltage range, time delay, and message count conditions are met will the control unit officially store and output the U025387 fault code.