B133613 - B133613 Refrigerant Temperature Sensor 3 Open Circuit

B133613 Refrigerant Temperature Sensor 3 Open Circuit Fault Deep Definition

DTC Group B1336 specifically refers to integrity verification of the refrigerant temperature feedback loop in the HVAC system. When the specific DTC is identified as B133613, this code indicates that the diagnostic algorithm inside the Left Domain Controller has identified an Open Circuit state while monitoring the feedback signal from Refrigerant Temperature Sensor 3 in real-time.

In vehicle electronic architecture, this control unit is responsible for collecting thermistor values at the evaporator or specific piping to calculate actual evaporation temperature and adjust compressor load. The open circuit fault means that communication between the sensor and control unit is interrupted, causing failure of the physical feedback loop, preventing the controller from obtaining real refrigerant thermodynamic parameters, thereby triggering system protection logic. This definition covers signal integrity assessment from the harness interface to internal controller pins.

Common Fault Symptoms

When Refrigerant Temperature Sensor 3 is determined to be open circuit, the HVAC control strategy will adjust, and driver-perceptible performance primarily includes:

• Reduced or Lost Cooling Capacity: The air conditioning compressor may enter an intermittent operation or forced stop state, leading to a significant drop in cold air circulation efficiency inside the cabin.
• HVAC System Function Degradation: Some automatic temperature control functions fail, and the system defaults to a Fail-safe Mode, usually retaining only fan blowing or fixed speed operation.
• Dashboard Warning Light Illumination: The corresponding DTC prompt is stored and displayed on the HVAC-related area of the instrument panel or central information display screen, accompanied by "Engine Malfunction Light" or "Service System" icons flashing.
• Abnormal Outlet Air Temperature: Due to missing sensor data, the air conditioning system cannot precisely control evaporator surface temperature, potentially leading to unstable outlet air temperature.

Core Fault Cause Analysis

Regarding the diagnostic logic for B133613 open circuit faults, potential root causes can be summarized into the following three technical dimensions:

• Hardware Component Failure: The thermistor element inside Refrigerant Temperature Sensor 3 undergoes open circuit damage, resulting in inability to output effective feedback signal. This is the direct manifestation of sensor body physical characteristic failure.
• Wiring and Connector Faults: The harness connecting the Left Domain Controller to the sensor experiences physical breaks, insulation wear or high impedance contact; simultaneously, oxidation, loosening or backing out of terminal connector pins leads to circuit connectivity interruption, causing open circuit voltage signal.
• Control Unit Logic Failure: Hardware circuits inside the Left Domain Controller responsible for processing input signals or its internal ADC sampling logic malfunction, unable to correctly identify sensor status, misjudging as high impedance open circuit signal.

Technical Monitoring and Trigger Logic

The determination of this fault code is based on a strict voltage threshold monitoring mechanism, where the system samples electrical characteristics of the sensor loop only under specific conditions.

• Monitoring Target: The control unit continuously reads the signal wire voltage value of Refrigerant Temperature Sensor 3. Under open circuit or open condition, due to missing signal loop reference potential, signal voltage is pulled up to high level state.
• Fault Trigger Condition: When Ignition Switch (Start/Stop Switch) is set to ON position and vehicle is powered in stationary or driving state, control system activates diagnostic monitoring program.
• Voltage Threshold Determination: System sets detection threshold of sensor output voltage above $4.95V$ as abnormal. Since normal temperature sensor signals usually lie within $0.1V$~$5.0V$ (depending on voltage divider ratio) linear range, continuously above $4.95V$ indicates harness open to ground or loss of ground reference, conforming to "Open Circuit" fault definition.
• Determination Cycle: This threshold monitoring is not triggered by single sampling but confirmed through specific drive cycle or consecutive multiple ignition cycles logic confirmation to ensure exclusion of false alarms caused by instantaneous electrical interference.