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Error code reference

LG Microwave Error Code E-b1

Cooling fan motor PCB temperature sensor open error.

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Cooling fan motor PCB temperature sensor open error.

First step from the service manual

Insert the temperature sensor.

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

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What E-b1 means on a LG microwave

The E-b1 error code on an LG microwave indicates a cooling fan motor PCB temperature sensor open error. This means the control board has detected an open circuit condition in the temperature sensor that monitors the PCB (printed circuit board) associated with the cooling fan motor. An open circuit in this context means the sensor's circuit is broken or incomplete, so the board receives no valid signal and cannot determine whether the cooling system is operating within safe thermal limits.

The cooling fan motor temperature sensor is a thermistor or thermocouple-type component responsible for monitoring heat levels at or near the fan motor and its associated circuit board. When this sensor is disconnected, damaged, or has developed an internal break, the microwave's control system registers the missing signal as a fault and triggers the E-b1 code. Because the microwave relies on this sensor to prevent overheating damage to the PCB and surrounding components, it will typically halt normal operation until the fault is resolved.

The first diagnostic step specified for this error is to inspect and reinsert the temperature sensor connector. In many cases, the sensor has simply become loose or disconnected from its socket on the PCB, particularly after shipping, vibration during use, or a previous repair. If reseating the connector does not clear the fault, the sensor itself may have failed internally and will need to be tested for continuity and replaced if an open condition is confirmed.

Source: manufacturer service documentation.

Common causes of E-b1

  1. 01

    Disconnected temperature sensor connector

    Wiring / connection

    The sensor's wiring harness connector may have come loose from its socket on the PCB, which is the most likely cause of an open circuit error. Reseating the connector firmly is the first recommended diagnostic step.

  2. 02

    Failed or open-circuit temperature sensor

    Part replacement

    The thermistor or temperature sensor component itself may have developed an internal break, producing a permanently open circuit regardless of connection status. Testing the sensor for continuity will confirm this failure.

  3. 03

    Damaged wiring harness

    Part replacement

    The wiring between the temperature sensor and the PCB may be cut, pinched, or broken, interrupting the circuit. Inspect the wire run for visible damage, especially where it passes near sharp edges or heat sources.

  4. 04

    Faulty cooling fan motor PCB

    Part replacement

    If the sensor and wiring both test correctly, the PCB itself may have a damaged sensor input circuit. This would prevent the board from reading a valid signal even when a functional sensor is connected.

See the test procedure for each cause

Frequently asked questions about E-b1

What does E-b1 mean on a LG microwave?
E-b1 indicates a cooling fan motor PCB temperature sensor open error. The microwave's control board has detected an open circuit in the temperature sensor that monitors the cooling fan's circuit board. This means the sensor is either disconnected, has a broken wire, or has failed internally. The microwave halts operation because it cannot confirm safe thermal conditions without a valid sensor signal.
How do I fix the E-b1 error on my LG microwave?
Start by unplugging the microwave and locating the temperature sensor connector on the cooling fan motor PCB, then firmly reseat the connector. If the error returns after power is restored, test the sensor for continuity to determine if it has failed internally and needs replacement. Inspect the wiring harness for any visible damage as well. If the sensor and wiring are both good, the PCB may require further diagnosis or replacement.
Is it safe to use my LG microwave while the E-b1 error is showing?
No, you should not attempt to operate the microwave while E-b1 is active. This error indicates the cooling system's temperature monitoring is non-functional, meaning the microwave cannot protect itself from overheating during a cooking cycle. Continued use without a working thermal sensor could cause damage to internal components or create a fire hazard.
Will resetting my LG microwave clear the E-b1 error?
A power reset by unplugging the unit for a few minutes may temporarily clear the error display, but the code will return if the underlying cause has not been corrected. The open circuit condition in the temperature sensor must be physically resolved, either by reseating the connector or replacing the faulty component, before the error will stay cleared.
How much does it cost to repair the E-b1 error on a LG microwave?
If the fix is simply reseating a loose connector, there is no parts cost and the repair can be done at home. If the temperature sensor needs replacement, parts typically range from around $10 to $40 depending on the model. If a professional repair technician is needed, expect to pay a service call fee plus labor, which can bring the total to somewhere between $80 and $200 or more depending on your location and the extent of the repair.

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