Powertrain, generic

P0E84 Auxiliary Cooling System Coolant Temperature Sensor A Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P0E84 is the high-voltage case for sensor A of the auxiliary loop: the signal sits near the reference voltage, which an NTC thermistor would only produce at extreme cold. Far more often the circuit is open, from an unplugged connector, a broken wire or a sensor with an internal break, or the signal line is shorted to a voltage source. The module then cannot judge the temperature of that loop and falls back to substitute values, which can make heater or pump control less precise. No manufacturer documents P0E84 publicly. Ford's 2019 hybrid summary uses P2185 for the equivalent fault of its heater-loop sensor ECT2, set after the driver signals a fault for 5 seconds. CARB wants temperature inputs tested for readings beyond their valid span. P0E83 is the low counterpart.

Likely causes

Unplugged connector or broken sensor wire
Sensor A open internally
Signal wire shorted to a voltage source

Symptoms

  • Check engine light
  • Scan tool shows the loop at minimum temperature
  • Less precise cabin heating

Repair estimate

DifficultyEasyDIY possible
Parts and labour€40–250
Time0.3–1.5 h

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

Parts involved

aux cooling coolant temp sensor awiring harness

Related codes

P0E81P0E82P0E83P2185

References: fordservicecontent.com, law.cornell.edu.