P157616 - P157616 Low Voltage Supply Voltage Too Low

P157616 Low Voltage Supply Voltage Too Low

Fault Depth Definition

DTC P157616 identifies the abnormal low state of low-voltage supply voltage in the vehicle electrical system. This DTC falls under the core monitoring scope of the power management control unit, used to feedback the energy supply stability of the powertrain or auxiliary systems. This definition covers the continuous monitoring mechanism when the entire vehicle's low-voltage battery group supplies power to core electronic control units, ensuring a normal working environment for internal logic operations and actuators. The code explicitly points to the technical state where supply voltage is below a set threshold, being an important parameter in vehicle electrical safety strategies.

Common Fault Symptoms

When the system detects conditions satisfying fault judgment criteria, car owners may perceive the following driving experience changes or instrument feedback:

• Dashboard low-voltage alarm light or power warning indicator light abnormally illuminated.
• On-board electronic system functions show intermittent failure, such as partial instrument backlight dimming, window control response delay, or communication interruption.
• The vehicle may exhibit a limited power state or be unable to start normally under specific operating conditions.
• Vehicle electrical load supply stability decreases during peak usage periods, accompanied by relay clicking sounds or voltage fluctuations.

Core Fault Cause Analysis

Based on existing diagnostic data, potential sources leading to P157616 are analyzed by dividing into the following three dimensions:

• Hardware Component Failure: Mainly involves battery unit internal cell performance degradation, abnormal increase in internal resistance, or physical short circuits. This type of fault directly causes open circuit voltage unable to maintain standard range, unable to provide stable power for loads.
• Wiring and Connector Faults: Refers to low-voltage supply wiring existing excessive contact resistance, open circuit phenomena, or connector pins oxidized loose, pin disengaging. Poor physical connection leads to abnormal voltage division, causing the controller-side collected voltage to be lower than actual battery voltage.
• Controller Logic Abnormality: Includes vehicle onboard charger output regulation abnormalities or power management control unit's own monitoring circuit reference drift. When charging modules cannot properly maintain busbar voltage, it triggers low voltage supply alarm.

Technical Monitoring and Trigger Logic

The generation of this DTC follows a strict system self-check algorithm, specific monitoring and trigger mechanisms are as follows:

• Monitoring Target: System collects instantaneous voltage values on the low-voltage supply bus in real-time ($V_{supply}$).
• Judgment Threshold: System internal sets a specific set threshold ($V_{threshold}$), used to define the lower limit of normal voltage range. This parameter is usually determined during calibration phase, to adapt to voltage fluctuation demands under different operating conditions.
• Trigger Logic: After system enters diagnostic state, when continuous detection of measured supply voltage is below set threshold ($V_{supply} < V_{threshold}$), generates DTC P157616.
• Specific Conditions: Fault judgment mainly conducted during vehicle ignition on and electrical load active period for dynamic monitoring. System only illuminates fault light and stores DTC after confirming abnormal signal exists continuously or exceeds allowed time window, to prevent false alarms due to sporadic interference.