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Error code reference

U-Line Ice Maker Error Code E4

Thermistor 4 open

U-Line codesU-Line ice maker codes

Thermistor 4 open - Ice Maker thermistor circuit is open.

First step from the service manual

Check thermistor connections and OHM test the thermistor.

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

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What E4 means on a U-Line ice maker

The E4 error code on a U-Line ice maker indicates that the Thermistor 4 circuit is open. Thermistor 4 is the ice maker thermistor, a temperature-sensing component responsible for monitoring the temperature within the ice making assembly. An open circuit in this thermistor means the control board is receiving no signal from the sensor, which prevents the unit from accurately regulating the ice making cycle. Without valid temperature data, the control board cannot confirm when ice has formed or when harvest conditions have been met, so it halts normal operation and triggers this fault code.

Thermistors are negative temperature coefficient (NTC) resistors, meaning their electrical resistance decreases as temperature increases. When functioning correctly, the thermistor provides a predictable resistance value to the control board. An open circuit condition means resistance has risen to an effectively infinite level, which the board interprets as a sensor failure rather than a valid temperature reading. This can result from a broken internal element within the thermistor itself, or from a loss of continuity anywhere along the wiring harness connecting the sensor to the control board.

The primary diagnostic approach is to inspect the thermistor wiring harness for loose, corroded, or disconnected connectors, and then perform an ohm test directly on the thermistor. A thermistor that reads OL (overload) or infinite resistance on a multimeter has failed internally and requires replacement. If resistance readings are within normal range, the fault likely lies in the wiring or connector terminals between the thermistor and the control board.

Source: manufacturer service documentation.

Common causes of E4

  1. 01

    Failed ice maker thermistor

    Part replacement

    The thermistor's internal resistive element has broken, creating an open circuit. This is confirmed by an infinite or OL resistance reading when the thermistor is tested with a multimeter.

  2. 02

    Loose or disconnected thermistor connector

    Wiring / connection

    The wiring harness connector at the thermistor or control board end has come loose, interrupting the circuit. Inspect both ends of the harness for connectors that are not fully seated.

  3. 03

    Damaged wiring harness

    Part replacement

    The wiring between the thermistor and the control board may have developed a break due to pinching, abrasion, or repeated flexing. Visually inspect the harness for frayed, cut, or pinched wire sections.

  4. 04

    Corroded or oxidized connector terminals

    Wiring / connection

    Moisture exposure inside the unit can cause connector pins and terminals to corrode, increasing resistance to the point of an open circuit. Check terminals for visible oxidation or pitting and clean or replace as needed.

See the test procedure for each cause

Frequently asked questions about E4

What does E4 mean on a U-Line ice_maker?
E4 indicates that the Thermistor 4 circuit, which is the ice maker temperature sensor circuit, is open. This means the control board is not receiving any signal from the ice maker thermistor. The unit cannot operate the ice making cycle safely without a valid temperature reading, so it displays this fault and stops production.
How do I fix the E4 error on my U-Line ice maker?
Start by inspecting the thermistor wiring harness and connectors for any loose, disconnected, or visibly damaged connections. Next, use a multimeter to ohm test the thermistor directly. If the thermistor reads infinite resistance or OL, it has failed and needs to be replaced. If the thermistor tests within a normal resistance range, trace the wiring back to the control board to find the break in the circuit.
Is it safe to continue using my U-Line ice maker when E4 is displayed?
It is not recommended to continue attempting to run the ice maker while the E4 fault is active. The unit cannot regulate its ice making cycle without a functioning thermistor, and operating it in this condition could lead to component damage. Address the fault before resuming normal use.
Will resetting my U-Line ice maker clear the E4 error?
A power reset may temporarily clear the displayed code, but the E4 error will return if the underlying thermistor circuit issue has not been resolved. The fault is tied to a hardware problem, not a software glitch, so the thermistor and its wiring must be tested and repaired before the error will clear permanently.
How much does it cost to repair a U-Line ice maker E4 error?
If only a wiring connection needs to be reseated or a terminal cleaned, repair costs may be limited to a service call fee, typically in the range of $75 to $150. If the thermistor itself needs replacement, parts costs are generally in the $20 to $60 range, with total repair costs including labor often falling between $100 and $250 depending on your location and the technician's rates.

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