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Error code reference

Bosch Dryer Error Code E:109

COM module (HomeConnect)

Bosch codesBosch dryer codes

COM module (HomeConnect) - general error.

First step from the service manual

Check wire harness between COM module and Operating Unit.

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

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What E:109 means on a Bosch dryer

Error code E:109 on a Bosch dryer indicates a general fault within the COM module, which is the HomeConnect communication module responsible for enabling Wi-Fi connectivity and smart home integration features. This module acts as a communication bridge between the dryer's main control system and external networks or devices. When the dryer's diagnostic system detects a breakdown in this communication chain, it logs E:109 to flag that the COM module is not functioning as expected.

The most common source of this fault is a disrupted or damaged wire harness running between the COM module and the Operating Unit (the control panel interface). Loose connectors, corroded terminals, pinched wiring, or a partially seated harness plug can all interrupt the signal path and trigger this error. Because the fault is labeled as a general error, it can also indicate an internal failure of the COM module itself, where the module's hardware or firmware has encountered a condition it cannot recover from.

Diagnosis should begin with a thorough inspection of the wire harness connecting the COM module to the Operating Unit. Check each connector for secure seating, and examine the wiring for visible damage such as abrasion, burns, or breaks. If the harness is intact and properly connected, the COM module itself should be considered as a suspect component requiring further bench testing or replacement.

Source: manufacturer service documentation.

Common causes of E:109

  1. 01

    Loose or disconnected wire harness

    Wiring / connection

    The harness connecting the COM module to the Operating Unit may have come loose at one or both connector ends. Inspect each plug for full seating and listen for a positive click when reseating connectors.

  2. 02

    Damaged wiring between COM module and Operating Unit

    Part replacement

    Physical damage such as pinching, abrasion, or heat exposure along the wire harness can break continuity in the communication circuit. Visually trace the entire harness length and use a multimeter to check for continuity on individual wires.

  3. 03

    Corroded or oxidized connector terminals

    Wiring / connection

    Moisture or age can cause oxidation on the harness connector pins, increasing resistance and degrading the signal between modules. Inspect terminals closely and clean or replace connectors showing visible corrosion.

  4. 04

    Failed COM module

    Part replacement

    If the wiring harness checks out as fully intact and properly connected, the COM module itself may have an internal hardware or firmware failure. A failed module will require replacement to clear the E:109 fault.

  5. 05

    Faulty Operating Unit

    Part replacement

    In cases where the COM module and wiring are confirmed good, a defective Operating Unit that cannot properly communicate with the COM module may be responsible for the error. This is the least common cause but should be considered after other components are ruled out.

See the test procedure for each cause

Frequently asked questions about E:109

What does E:109 mean on a Bosch dryer?
E:109 indicates a general error in the COM module, which is the HomeConnect Wi-Fi and smart communication module in the dryer. The fault signals that communication between the COM module and the Operating Unit has failed or is disrupted. The dryer's core drying functions may still operate, but smart connectivity features will be affected. Diagnosis starts with inspecting the wire harness between these two components.
How do I fix E:109 on my Bosch dryer?
Begin by unplugging the dryer and locating the wire harness that runs between the COM module and the Operating Unit. Check that all connectors are fully seated, and inspect the wiring for any visible damage or corrosion. If the harness appears intact, the COM module itself may need to be replaced. A qualified appliance technician can confirm which component is at fault through further testing.
Will resetting my Bosch dryer clear the E:109 error?
A power reset may temporarily clear the E:109 code, but if the underlying issue such as a loose harness, damaged wiring, or failed COM module is still present, the error will return. Resetting is a reasonable first step, but a physical inspection of the COM module wiring is necessary to achieve a lasting repair.
Is it safe to use my Bosch dryer when E:109 is displayed?
E:109 is specifically related to the HomeConnect communication module and does not necessarily indicate a problem with the dryer's heating or mechanical systems. In many cases, the dryer can still be used for normal drying cycles while the COM module fault is present. However, it is best to have the error diagnosed promptly, as unaddressed wiring issues could develop further over time.
How much does it cost to repair a Bosch dryer E:109 error?
Repair costs vary depending on the root cause. If the fix involves only reseating a connector or cleaning terminals, the cost may be limited to a diagnostic service call, typically in the range of $75 to $150. If the COM module itself requires replacement, parts and labor combined can range from $150 to $350 or more depending on parts availability and local labor rates.

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