P0CEF: Hybrid/EV Electronics Coolant Temperature Sensor A Circuit Range/Performance

What does P0CEF mean?

The sensor stays electrically within range but reports a temperature that does not fit its surroundings. GM uses two kinds of comparison. In the 2011 Volt and the ELR it is checked against the high-voltage charger temperature with the pump running at 30 % or more for over 60 or 300 s; the limit is 38 to 40 °C (2011) or 35 °C (ELR). From the 2016 Volt on the test runs once after a long rest (propulsion off over 18,000 or 21,600 s, pump and A/C off for 3,600 s) and compares with outside air, transmission fluid and A/C high-side temperature; limits are 27/27/28 °C, 21/35 °C in 16OBDG02. GM uses 32 of 40 samples or 8 s in 10 s, Type B, two trips. Hard circuit faults are P0CF0/P0CF1, noise P0CF2. A wrong reading misleads the cooling and power limits.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Malfunction indicator lamp on, often without noticeable drivability change
• Electronics coolant pump runs at odd times or longer than usual
• Occasional power or charging limitation

Common causes

• High Sensor element drifted and reads offset from the real coolant temperature
• Medium Added resistance from corroded terminals shifting the signal
• Medium Genuine temperature gap from poor flow or air in the electronics loop
• Low Comparison sensor (charger, outside air or transmission fluid) reading wrong without its own code

Likelihood is a general estimate across vehicles; your make and model may differ.