Open circuit or poor connection at the evaporator temperature sensor connector; Faulty evaporator temperature sensor; Damaged, corroded or broken wiring in the signal or ground circuit (open circuit); Signal wire shorted to a voltage supply; Sensor not seated correctly in the evaporator or climate housing after previous work; Fault in the climate control or engine control unit.

P0538

A/C Evaporator Temperature Sensor Circuit High.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
38: FaultThe specific fault in that area

What it means

P0538 is the generic code for a high input on the A/C evaporator temperature sensor circuit. The control unit saw the sensor signal voltage rise above the expected range, usually because the circuit is open, the sensor is faulty or the signal wire is shorted to a voltage supply. Which module monitors this sensor, and the exact trip thresholds, vary by model.

Symptoms

A/C blows warm or does not cool properly
A/C compressor does not engage or cycles erratically
A/C warning or fault message on some models
Evaporator freezing up with reduced airflow if the compressor runs without proper control
Climate control not responding correctly to temperature settings

Possible causes

Open circuit or poor connection at the evaporator temperature sensor connectorlikely
Faulty evaporator temperature sensorlikely
Damaged, corroded or broken wiring in the signal or ground circuit (open circuit)possible
Signal wire shorted to a voltage supplypossible
Sensor not seated correctly in the evaporator or climate housing after previous workpossible
Fault in the climate control or engine control unitrare

How to diagnose

Read all stored codes and freeze frame data, then note whether the fault is current or intermittent
Check live data for the evaporator temperature reading and see if it sits at an extreme, implausible value
Inspect the sensor connector and wiring for damage, corrosion, bent pins or water ingress
Unplug the sensor and check the live reading changes as expected; consult model-specific data for the correct behaviour
Measure the sensor resistance and compare it with the manufacturer specification at a known temperature
Check the sensor reference voltage and ground at the connector with the ignition on
Test the signal wire for continuity and for shorts to voltage or ground between the sensor and control unit
Clear the code and road test to see if it returns

How to fix

Repair or replace damaged wiring and terminals in the sensor circuit
Clean, reseat or replace a corroded or loose connector
Replace the evaporator temperature sensor if its resistance is out of specification
Refit the sensor correctly in its housing if it is loose or misplaced
Repair any short to voltage found in the signal wire
Replace or have the control unit checked only after the wiring and sensor have been proven good

Can I keep driving?

Low severity

The car is generally safe to drive, but the A/C may not work properly. Book it in for repair at your convenience.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.