P1438

Ford

A/C Evaporator Air Temperature Circuit Range/Performance

Definition source: Manufacturer reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Low Severity

The A/C evaporator air temperature sensor reports temperature near the evaporator so the vehicle’s control system can manage cooling and help prevent evaporator icing. This code means the reported circuit value or its response is outside the expected range. It does not prove the sensor itself has failed; exact operation depends on the vehicle.

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⚠️ Before You Begin (Safety First)

This fault usually affects A/C operation rather than basic drivability. If the climate system cannot clear windshield fog or frost and visibility is reduced, pull over safely. Do not open refrigerant lines or handle refrigerant without proper equipment and training.

Common Symptoms

  • A/C may cool poorly or inconsistently if the control system receives an inaccurate evaporator temperature reading.
  • The compressor may be controlled or cycled differently than expected, depending on the vehicle’s system strategy.
  • Cooling may be reduced if the system responds to a reading that suggests the evaporator is too cold or too warm.
  • The evaporator could be more prone to icing if temperature feedback does not allow the system to manage cooling correctly.
  • There may be no noticeable symptoms, especially if the fault is intermittent or the system continues operating normally.

Common Causes

  • A failing evaporator air temperature sensor may report an inaccurate value or respond improperly as temperature changes.
  • A loose, damaged, or corroded connector can interrupt or distort the sensor signal.
  • Damaged wiring or a circuit fault can cause an implausible reading or intermittent signal.
  • A genuine temperature or airflow condition at the evaporator may contribute to a reading outside the expected range.
  • A control-module or related circuit problem is possible, but should be considered only after the sensor and wiring are checked.

Diagnostic Steps

  1. Note whether the A/C cools normally and whether the problem is intermittent; this helps describe the conditions when the fault occurs.
  2. With the vehicle off, visually check accessible wiring and connectors for looseness, damage, or corrosion. Do not pull on wires or force a connector.
  3. Check whether cabin airflow is restricted by a dirty cabin air filter, if the vehicle has an accessible filter; restricted airflow can affect A/C performance.
  4. If a suitable scan tool is available, observe the evaporator temperature reading and note whether it changes plausibly during A/C operation. Do not treat one reading as proof of a failed sensor.
  5. Have a qualified technician test the sensor circuit and A/C system using the wiring diagram and procedures for the exact model, year, and engine. Avoid opening refrigerant lines.

When to Call a Professional

Check the evaporator temperature reading in scan data and see whether it changes plausibly as conditions change. Inspect the sensor connector and wiring, then test the circuit and sensor response using model-specific service information. Confirm airflow and A/C system operation before replacing parts; the code alone does not identify the failed component.

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Commonly Asked Questions

Does P1438 mean the evaporator temperature sensor must be replaced?

No. The code identifies a range/performance problem in the circuit. The sensor, connector, wiring, operating conditions, or related control circuitry may be involved.

Can I keep driving with this code?

Usually, the fault affects air conditioning rather than engine operation. Do not drive if poor windshield defogging or defrosting leaves visibility unsafe.

Can this code cause weak or inconsistent cooling?

It can. An inaccurate temperature signal may affect how the system manages cooling, but airflow and other A/C system problems can produce similar symptoms.

How is the fault distinguished from a bad sensor?

A technician checks the scan-data reading and its response, inspects the connector and wiring, and tests the circuit before deciding whether the sensor is faulty.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.