B1233 — Refrigerant temperature sensor (B12/1)

Causes

• Failed refrigerant temperature sensor (B12/1)
• Open, shorted, or high-resistance wiring in sensor circuit
• Corroded or loose connector at sensor or HVAC control module
• Water ingress or contamination of connector/sensor
• Intermittent connection due to chafing or broken wire
• Control module input fault (rare)

Symptoms

• Reduced or no A/C cooling, or A/C cycles on/off
• HVAC fault warning or refrigerant temperature message
• Compressor disabled or operating intermittently
• Blowing warm air from vents or slower-than-normal cabin cooling
• Stored or pending DTCs related to HVAC/AC control

What to check

• Read and record DTC(s) and freeze frame data with a scan tool
• Visually inspect sensor location, connector, and wiring for damage or corrosion
• Backprobe connector to verify reference voltage and ground presence with ignition on
• Measure sensor resistance at ambient temperature and compare to expected NTC curve
• Wiggle harness while observing live data for intermittent changes
• Check for related DTCs (compressor control, evaporator temp, HVAC module)

Signal parameters

• Sensor type: typically an NTC thermistor (resistance decreases as temperature rises)
• Typical resistance behavior: higher ohms at low temperature, lower ohms at high temperature (example: ~10 kΩ at ~25°C — verify OEM spec)
• Expected voltage at control module/sensor circuit commonly in the range ~0.5–4.5 V depending on temperature and system
• No voltage (open) or near battery/ground (short) indicates wiring/connector fault

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