U025387 - U025387 Lost Communication with Compressor

Deep Definition of U025387 Fault Code

This fault code ( U025387 ) belongs to in-vehicle communication network class diagnostic codes ( U codes ), mainly indicating abnormal data interaction between domain controllers inside the vehicle. Specifically, this fault indicates that the vehicle's Left Domain Controller failed to successfully receive network messages sent by the Electric Compressor. In vehicle electronic architecture, the operation of the air conditioning system relies on stable high-speed data exchange between control units. When this communication link is interrupted or times out, the system will determine that network integrity is damaged and record this fault definition.

Common Fault Symptoms

When this fault code is stored and lit up, drivers may observe the following manifestations related to comfort systems:

• Vehicle air conditioning system's cooling function failure, blowing hot air or no airflow.
• Warning lights related to powertrain or communication faults may appear on the dashboard (if applicable).
• The vehicle electronic control system may enter a safety protection mode, limiting compressor output.
• In extreme conditions, it may cause the air conditioning system to default to switching to heater or turning off the cooling cycle.

Core Fault Cause Analysis

Based on diagnostic logic and electrical principles, potential factors leading to U025387 fault generation are mainly concentrated in the following three dimensions:

• Hardware Component Failure: including fuse blowout for electric compressor power supply, or internal electronic module damage/control unit dead of the Electric Compressor itself.
• Wiring and Connector Physical Connection: involving harness or connector faults connecting Left Domain Controller and Electric Compressor, such as open circuit, short circuit, pin corrosion or poor contact, leading to signal transmission interruption.
• Controller and Network Communication Logic: including CAN network communication fault (bus voltage abnormal, terminal resistance mismatch, etc.), and the left domain controller's network management strategy unable to identify or parse compressor data frames.

Technical Monitoring and Trigger Logic

Vehicle On-Board Diagnostic system (OBD) judges this fault based on the following specific monitoring targets and conditions:

• Monitoring Target: Left Domain Controller real-time monitoring of received Electric Compressor Message frequency integrity and validity. The system does not monitor specific signal voltage values, but determines communication status through data frame arrival within a time window.
• Fault Setting Condition: When ignition switch is in ON position, the system enters diagnostic working mode. If Left Domain Controller fails to receive electric compressor messages within a certain time, it is judged as communication loss. At this point, control unit internal timer times out and resets, storing the DTC.
• Fault Trigger Condition: Formal generation and storage of fault code must be completed under premise of ignition switch in ON position, ensuring vehicle is powered on and system is interactive.