P0538: A/C Evaporator Temperature Sensor Circuit High

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.

Low severity. Can I keep driving?Yes, you can keep driving. The air conditioning may not work.

Symptoms

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

Most likely causes

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

What to check, in order

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

Check the sensor pressure in live data
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Check the relay and connector
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 P0538 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
5: Speed and idle
38: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0538?

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

What causes code P0538?

The most common causes are: connector off or corroded, wire open; sensor open internally; ground line open.

Related codes

Sources

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.