U0629

Code

Generic U — Network/User

Lost Communication With A/C Refrigerant Temperature Sensor “B”

Brand: Generic

Type: U — Network/User

Views: UK: 23 EN: 34 RU: 36

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Retrieve freeze-frame and related codes; check whether code is current or intermittent
Visually inspect sensor connector and wiring for corrosion, damage, or water intrusion
Check for proper power and ground to the sensor (fuse and circuit integrity)
Backprobe sensor connector and measure resistance/voltage while varying temperature if accessible
Use scan tool to view live sensor data and communication bus activity (LIN/CAN)
Wiggle wiring harness near connectors while monitoring for code/parameter changes

Type: commonly a thermistor (analog) or a digital sensor on LIN/CAN. Verify vehicle service data for exact type.
Thermistor behavior: resistance decreases as temperature rises. Typical order-of-magnitude at 25°C: ~1–20 kΩ (vehicle-specific).
Open-circuit threshold: very high resistance (>>100 kΩ) or infinite; short-circuit threshold: very low (tens of ohms).
Analog voltage-type sensors: approximate range 0.5–4.5 V proportional to temperature (vehicle-specific).
Digital/LIN: single-wire communication idle/bus levels vary; CAN: differential bus ~2.5 V nominal on both lines. Check for traffic with a bi-directional scan tool.

Confirm code and note freeze-frame data. Check for additional U-codes or HVAC/A/C related codes.
Visually inspect sensor 'B' connector and harness for corrosion, bent pins, water, or mechanical damage. Repair as needed.
Verify fused power and ground for sensor and HVAC control module. Check fuses and measure voltage to the sensor connector with ignition on.
Identify sensor type from service data (thermistor vs digital). If thermistor: unplug sensor and measure resistance across sensor terminals at known ambient temperature and compare to specification. If reading is open or short, replace sensor.
If analog: backprobe sensor with connector connected and measure voltage while changing temperature (warm/cold) to confirm sensor response. If no response but power/ground present, suspect sensor or high-resistance connection.
If digital (LIN/CAN): use a scan tool to check for sensor 'B' data, bus voltage, and traffic. Check termination resistances and inspect wiring for shorts to other lines.
Wiggle test wiring and connectors while monitoring live data and watch for intermittent dropouts. Repair/replace damaged harness sections or connectors.
If wiring and sensor check good, test/reprogram or swap HVAC/A/C control module (if allowed by manufacturer) to confirm module-side fault.
After repairs, clear codes, perform A/C operability test and road or operational test to confirm code does not return.

Damaged connector or wiring to A/C refrigerant temperature sensor 'B' (most common)
Failed sensor (thermistor open/short or internal electronics failure)
Poor ground or lost sensor supply voltage
Fault on LIN/CAN data line or module-side driver
Faulty HVAC/A/C control module