P0538 low

Evaporator Temperature Sensor Circuit High

The P0538 code means the vehicle's onboard diagnostic system has detected: Evaporator Temperature Sensor Circuit High. This is a low severity code.

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Keep driving?: Yes, but fix soon
DIY difficulty: hard
Estimated cost: $100 - $500 (parts and labor)

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Common Symptoms

Check Engine Light on
Evaporator may freeze up
AC runs constantly without cycling
Ice buildup on evaporator

Probable Causes (Ranked by Likelihood)

Open circuit in evaporator temperature sensor wiring Very High
Failed sensor with open internal circuit High
Disconnected evaporator temperature sensor connector Moderate
Corroded pins causing high resistance in sensor circuit Moderate

Step-by-Step Diagnostic Procedure

Read evaporator temperature sensor value; an extremely warm reading when AC is running cold confirms circuit high
Check sensor connector for disconnection or corrosion
Measure sensor resistance; an open reading (infinite ohms) confirms sensor failure
Inspect wiring for breaks, especially where it passes through the firewall or HVAC housing

Frequently Asked Questions

Why does the evaporator freeze with P0538?

When the sensor reads high (falsely indicating a warm evaporator), the system never cycles the compressor off to prevent freezing. The compressor runs continuously, dropping the evaporator temperature below freezing and causing ice buildup.

How do I know if my evaporator is frozen?

A frozen evaporator blocks airflow through the vents. You may notice reduced or no airflow from the vents even with the blower on high, followed by a gush of water when the ice melts after shutting off the AC.

What does circuit high mean for P0538?

Circuit high means the sensor signal voltage is above the expected maximum, making the system read an extremely warm temperature. This is typically caused by an open circuit (broken wire or disconnected sensor) where the pull-up voltage reads through.