Powertrain, generic

P0EC4 A/C Refrigerant Temperature Sensor B Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modeNo

P0EC4 is a plausibility fault: sensor B delivers a voltage inside its normal window, yet the temperature it reports does not agree with other information. No manufacturer documents P0EC4 publicly. A well-described pattern comes from GM's 2012 Volt (P153B, Type B): once the compressor has been off for over an hour, the low-side refrigerant temperature must lie within 10 degrees Celsius of the raw ambient temperature and of the value derived from high-side pressure; the check runs only when no circuit codes are active. A drifting sensor, poor thermal contact or a wrong charge can fail such a comparison. The A/C usually still works but may be controlled poorly. Electrical faults of sensor B: P0EC1 to P0EC3.

Likely causes

Sensor B drifting out of tolerance
Sensor not seated properly on the pipe, poor thermal contact
Incorrect refrigerant charge shifting the comparison values

Symptoms

  • Uneven or weak cooling, compressor cycling oddly
  • Fault often appears only after a long standstill

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–500
Time0.5–2.5 h

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

Parts involved

ac refrigerant temp sensor bhvac control module

Related codes

P0EC1P0EC2P0EC3P0EBFP0531

References: gsi.ext.gm.com, law.cornell.edu.