Network, generic

U0627 Lost Communication With A/C Refrigerant Temperature Sensor A

Check engine lightUsually off

EmissionsNot relevant

Drive cycleNot required

Limp modeNo

Refrigerant temperature matters most where a controller adjusts superheat itself, as with electronic expansion valves and heat pumps; it also guards against overheated discharge gas. U0627 is set once the digital temperature value from sensor A is no longer received. Many suppliers build temperature and pressure into one housing; Sensata, for example, offered such R744 sensors with LIN, PWM or analog output. If U0626 appears at the same moment, the shared plug, LIN line or supply of that combined part is the first suspect; if only U0627 is present, the temperature channel or a separate sensor is more likely. No manufacturer documents U0627 publicly. Depending on the strategy, cooling or heat-pump output drops or stops. Analog equivalents are P0EBC to P0EBF.

Likely causes

Connector, LIN line or supply of a combined pressure/temperature sensor faulty

Temperature channel or sensor electronics failed

Climate or thermal controller no longer polls the sensor (software or LIN master fault)

Symptoms

Reduced cooling or heat-pump output
Heat-pump mode unavailable, auxiliary heater takes over
A/C fault message

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€50–400

Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

ac refrigerant temp sensor avehicle bus wiring

References: archive.r744.com, static.nhtsa.gov, en.wikipedia.org, law.cornell.edu.