Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P0538 A/C Evaporator Temperature Sensor Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The evaporator temperature sensor, an NTC thermistor behind the evaporator, prevents icing: near 0–3 °C the compressor is switched off or reduced. Usually the climate module reads it and reports body codes; P0535–P0539 only arise where the engine module controls the compressor and reads the sensor. P0538 means the signal voltage is above its limit – an open sensor, signal or ground line, or a short to positive; with an NTC that reads as implausibly cold, so the system assumes icing and usually locks out the compressor. No manufacturer document available to us uses this code; the description follows CARB's input component rules.

Likely causes

Connector off or corroded, wire open
Sensor open internally
Ground line open
Short to positive

Symptoms

  • Air conditioning not cooling (compressor locked out)
  • Vents blowing warm
  • Usually no check engine light

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–400
Time0.5–4 h

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

Parts involved

evaporator temperature sensorsensor wiringengine control module

Related codes

P0535P0536P0537P0539

References: en.wikipedia.org, hella.com, law.cornell.edu.