P0EC4: A/C Refrigerant Temperature Sensor B Range/Performance

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.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the sensor pressure in live data
2. Compare the reading with other engine data while varying the engine speed.
3. Check the relay and connector
4. Have the refrigerant charge and any leaks checked at a repair shop authorized to handle refrigerant

Good to know

• Repair difficulty: medium

What each character of P0EC4 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• E: Subsystem depends on the code range
• C4: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0EC4?

Yes, you can keep driving. The air conditioning may not work.

What causes code P0EC4?

The most common causes are: sensor B drifting out of tolerance; sensor not seated properly on the pipe, poor thermal contact; incorrect refrigerant charge shifting the comparison values.

Related codes

• P0EC1A/C Refrigerant Temperature Sensor B Circuit
• P0EC2A/C Refrigerant Temperature Sensor B Circuit High
• P0EC3A/C Refrigerant Temperature Sensor B Circuit Low
• P0EBFA/C Refrigerant Temperature Sensor A Range/Performance
• P0531A/C Refrigerant Pressure Sensor A Circuit Range/Performance

Sources

• gsi.ext.gm.com: 12OBDG01A HYBRID Diagnostics
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.