P0EC1: Air Conditioning Refrigerant Temperature Sensor B Circuit
What to do
Expect a real drop in winter range if the car has a heat pump — losing it forces resistive heating, which draws several kilowatts from the traction battery. The cabin will still get warm. In summer, watch for slower rapid charging if this circuit also cools the battery.
What this code means
The circuit for one of the refrigerant temperature sensors is faulty.
Measuring the refrigerant's own temperature is a thing conventional air conditioning does not bother with, and the reason it appears here is the heat pump.
A conventional system only has to make the cabin cold, so knowing the evaporator temperature is enough — it exists to stop the evaporator icing up. A heat pump has to run the same circuit backwards to heat the cabin, extracting warmth from outside air that may be at freezing point, and that is a far more delicate operation.
It works because refrigerant boils at a temperature set by its pressure, so at low enough pressure it will boil — absorbing heat — even in air well below zero. Managing that means knowing where the refrigerant actually is on its pressure-temperature curve, at more than one point in the circuit, which is why there are two of these sensors rather than one.
Which makes a fault here a winter problem on a heat-pump car. Losing the measurement means the car cannot run the heat pump safely, so it falls back to resistive heating — and resistive heating on an electric car costs real range, several kilowatts drawn straight from the traction battery. The symptom is a car that has suddenly become much worse in cold weather with the cabin still warm.
On many vehicles the same circuit also chills the battery, so the summer version is rapid charging that has slowed.
The base circuit fault: no plausible signal.
Likely causes
Start here
- Faulty air conditioning refrigerant pressure sensor · specialist
- Corroded or loose connector · specialist
- Open circuit in sensor wiring · specialist
Less common
- Low refrigerant charge · moderate
- Damaged wiring harness · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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