mypros+
Error code reference

Maytag Washer Error Code F40

ATC Thermistor Open/Short

Maytag codesMaytag washer codes

ATC Thermistor Open/Short – the ATC (Automatic Temperature Control) thermistor is detected to be open or shorted.

First step from the service manual

See TEST #5, page 5.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

MyPros+ Max

Get the full diagnostic procedure for F40.

  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What F40 means on a Maytag washer

The F40 error code on a Maytag washer indicates a fault with the ATC (Automatic Temperature Control) thermistor, which has been detected as either open or shorted. The ATC thermistor is a temperature-sensing resistor that monitors incoming water temperature and communicates that data to the control board. This allows the washer to precisely blend hot and cold water to reach the desired wash temperature. When the control board reads a resistance value that falls outside the expected range, either extremely high resistance indicating an open circuit or near-zero resistance indicating a short, it sets the F40 code and may interrupt the wash cycle to prevent temperature-related errors.

An open thermistor means the electrical circuit through the component has been broken, often due to a failed sensor, a broken wire, or a disconnected connector. A shorted thermistor means the circuit is allowing current to flow without proper resistance, which can result from internal component failure or insulation breakdown in the wiring. Both conditions render the thermistor unable to send accurate temperature data to the control board.

Diagnosing this fault should begin with the procedure outlined in TEST #5 of the technical service documentation. That test covers checking the thermistor resistance and inspecting the associated wiring harness and connectors. A proper resistance measurement at the thermistor terminals will confirm whether the sensor itself has failed or whether the fault lies in the wiring or connections between the sensor and the control board.

Source: manufacturer service documentation.

Common causes of F40

  1. 01

    Failed ATC Thermistor

    Part replacement

    The thermistor itself has failed internally, resulting in an open or shorted resistance reading. Measuring resistance at the thermistor terminals will show a value well outside the expected range if the component has failed.

  2. 02

    Broken or Damaged Wiring Harness

    Part replacement

    The wiring between the ATC thermistor and the control board may have a break, pinch, or burned section that causes an open or short circuit. Visually inspect the harness for damage and test for continuity along each wire.

  3. 03

    Loose or Corroded Connector

    Wiring / connection

    A connector at either the thermistor or the control board may have come loose or developed corrosion, interrupting the signal. Disconnecting and reseating connectors while checking for corrosion or bent pins can resolve this without replacing parts.

  4. 04

    Water or Moisture Intrusion

    Wiring / connection

    Moisture reaching the thermistor connector or wiring can cause short circuit conditions or accelerate corrosion. Inspect the connector housing and surrounding area for signs of water exposure.

  5. 05

    Faulty Control Board

    Part replacement

    If the thermistor and wiring both test within spec, the control board may be misreading the sensor signal due to a failed input circuit. This is less common and should only be considered after the thermistor and harness have been ruled out.

See the test procedure for each cause

Frequently asked questions about F40

What does F40 mean on a Maytag washer?
F40 means the washer has detected that the ATC (Automatic Temperature Control) thermistor is either open or shorted. This thermistor is responsible for measuring water temperature so the machine can blend hot and cold water accurately. The control board identified a resistance reading outside the acceptable range and triggered the fault code. The washer will need the thermistor, wiring, and connections inspected to find the cause.
Can I fix the F40 error code myself?
Some causes of F40 are DIY-friendly, such as reseating a loose connector or inspecting the wiring harness for visible damage. However, if the thermistor itself has failed, it will need to be replaced, which requires locating the correct part and accessing internal washer components. Following the diagnostic procedure in TEST #5 is the recommended starting point to determine what specifically has failed before ordering any parts.
Is it safe to use my Maytag washer with an F40 error code?
Running the washer with an active F40 code is not recommended. Without a functioning ATC thermistor, the control board cannot accurately regulate water temperature, which can result in clothes being washed at unintended temperatures. Continuing to run the washer may also mask additional issues if the wiring fault worsens. It is best to diagnose and resolve the fault before resuming normal use.
How much does it cost to repair an F40 error on a Maytag washer?
Repair costs vary depending on the root cause. If the fix is simply reseating a connector, there is no parts cost. A replacement ATC thermistor typically costs in the range of $15 to $50 for the part alone. If the control board needs to be replaced, costs can range from $100 to $300 or more for the part. Adding professional labor generally brings the total repair cost to somewhere between $100 and $400 depending on the fault.
Will resetting the washer clear the F40 error code?
A reset may temporarily clear the F40 code from the display, but it will return if the underlying fault with the ATC thermistor or its wiring has not been corrected. Resetting without repairing gives no information about whether the problem is resolved. The proper approach is to perform the TEST #5 diagnostic procedure to identify and fix the actual cause, after which the code should clear and not return.

Related Maytag washer codes

All Maytag washer codes
View all 404 Maytag washer codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass