P151500 - P151500 Coolant Temperature Sensor Fault

P151500 Deep Definition of Water Temperature Sensor Fault

In new energy vehicle electronic control systems, P151500 is a diagnostic trouble code used to identify abnormalities in the monitoring of key parameters of the on-board thermal management system. This fault code primarily involves the temperature monitoring unit in the On-Board Charger (OBC) cooling circuit. Its core role lies in providing real-time feedback on the physical location and rotational speed of the motor or charging module, as well as the thermal status of the internal heat dissipation fluid. When the control unit receives signal data from the water temperature sensor, it compares it with an actual thermodynamic model to ensure no overheating damage occurs during high-voltage conversion.

The generation of this DTC means the control system has already identified that physical parameters within the cooling waterway have exceeded preset safe logic, but this does not necessarily mean the vehicle has lost all power, but rather triggers a specific safety monitoring procedure. The Control Unit (ECU) and the main control chip inside the On-Board Charger collaborate to handle this feedback signal; once abnormal data flow is detected, the system will record this DTC and may adjust power output strategies to ensure the long-term reliability of the battery pack and charging components.

Common Fault Symptoms

Regarding the recording and display of P151500 fault codes, users may observe the following phenomena during actual driving or charging processes:

• Dashboard Fault Indicator Light Prompt: When the system detects an anomaly, the dashboard usually illuminates the corresponding fault light (such as battery warning, charging system warning) to warn the driver to pay attention to the system status.
• Record DTC without Interrupting Function: Although the system has judged the existence of a fault and generated P151500, the vehicle usually allows "normal charging" before entering the fault protection mode. This means that when not reaching more severe failure thresholds, the On-Board Charger can still maintain basic work, but the DTC code will remain in the system log for subsequent diagnosis.
• Thermal Management System Warning: If the fault persists or temperature further rises, it may be accompanied by indirect feedback such as abnormal AC system or cooling fan speed, leading to limited capability of adjusting the vehicle interior environmental temperature.
• Limited Charging Power: For safety reasons, the control unit may dynamically manage input current in the background; although "normal charging" is displayed under some conditions, actual power may already be below the rated upper limit.

Core Fault Cause Analysis

According to current system data, the fundamental logic attribution of P151500 fault lies in the abnormal response of internal components within the On-Board Charger. The following professionally analyze the cause of failure from three dimensions: hardware, wiring and controller:

• Hardware Component Failure (Inside OBC): Fault may originate from the performance degradation of the water temperature sensor itself inside the OBC module, leading to signal output drift or open circuit; or it is that the physical state of the cooling waterway at the sensor installation location has changed (such as blockage, crystallization), leading to actual temperature collection lag. In addition, if the processing circuit inside the On-Board Charger has component aging, it can also lead to voltage signals unable to be correctly transmitted to the control unit.
• Wiring and Connector Connection Anomaly: Although original data mainly points to internal faults, in actual physical diagnosis, when there is high impedance, poor contact or shielding layer interference on the power supply line ( $12V$ or $5V$ reference voltage) of the sensor loop and signal ground lines, it will also cause the control unit to read incorrect water temperature values. Connector pin oxidation and corrosion may lead to current transmission obstruction.
• Controller Logic Operation Anomaly: The control chip (MCU/MPU) inside the On-Board Charger may have logic judgment errors, unable to correctly parse sensor analog signals. Under certain specific operating conditions, the filtering algorithm inside the controller may mistakenly judge instantaneous interference as effective fault values, thereby incorrectly triggering P151500 recording.

Technical Monitoring & Trigger Logic

The generation of this DTC follows a strict logic control flow, where the system activates in-depth monitoring of waterway temperature only under specific high-voltage operation states:

• Operation Condition Limitation: The effective state for fault judgment is strictly limited to one of the following two operating modes: the vehicle is in AC Charging mode or Vehicle-to-Load Discharge mode. In non-charging or non-discharge modes, this monitoring logic usually does not activate.
• Monitoring Target and Threshold Determination: The system collects liquid temperature data inside the cooling waterway in real time and dynamically compares it with the specified threshold in the control strategy.
• Trigger Mechanism and Fault Definition: Only when satisfying the above operation conditions, if the system detects that the waterway temperature value exceeds the specified threshold, the diagnostic program immediately judges it as abnormal and generates P151500 fault code in the next CAN bus cycle.
• Data Recording Strategy: Once triggered, the control unit not only stores the fault status in the current cycle but also records freeze frame data (Freeze Frame) under vehicle sleep mode, including water temperature sampling values and voltage data at the triggering moment, for subsequent technical support root cause analysis.