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U0628 Lost Communication With A/C Refrigerant Pressure Sensor B

Check engine lightUsually off

EmissionsNot relevant

Drive cycleNot required

Limp modeNo

A second pressure transducer appears mainly in heat pumps and CO2 (R744) systems, where both the low and the high side are measured to control efficiency and detect leaks; the Sensata R744 presentation lists heat-pump control and leak diagnosis among those uses. U0628 means that the digital pressure value from sensor B no longer reaches its controller. If sensor A still reports while B is silent, the fault is likely in B's own branch, plug or electronics rather than in the controller. No manufacturer documents U0628 publicly. Losing the second pressure value usually ends heat-pump operation or forces a conservative compressor mode. Hardwired faults of the same sensor show as P2515 to P2518 or P05E2; disagreement between A and B is P2CD4.

Likely causes

Damaged LIN, supply or ground wire in the branch to sensor B

Wet, corroded or loose connector at sensor B

Sensor B electronics failed

Symptoms

Heat pump does not heat, cabin heating relies on the auxiliary heater
Weak or no A/C cooling
A/C or thermal system warning message

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€60–500

Time0.5–3 h

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

Parts involved

ac refrigerant pressure sensor bvehicle bus wiring

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