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Error code reference

Bosch Dryer Error Code E:0120

Power Unit

Bosch codesBosch dryer codes

Power Unit - variant coding error (4-digit equivalent of E:67).

First step from the service manual

Perform flashing of Operating Unit and Power Unit.

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

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What E:0120 means on a Bosch dryer

Error code E:0120 on a Bosch dryer signals a variant coding mismatch between the Power Unit (the main control board responsible for motor drive, heating, and power distribution) and the Operating Unit (the user interface and program control board). This is the 4-digit equivalent of the abbreviated code E:67 and indicates that the two control boards do not recognize each other as compatible variants. Variant coding is a software-level identifier embedded in each control unit that tells the dryer's control system which hardware configuration, regional specification, and feature set is installed. When these identifiers do not match, the dryer cannot operate safely or correctly and will halt with this fault.

This type of error most commonly occurs after one or both control boards have been replaced with a unit carrying a different firmware or variant code than the original. It can also appear if a software update was interrupted or applied incorrectly to one unit but not the other, leaving the two boards out of sync. In rare cases, a corrupted firmware state following a power surge or voltage fluctuation can cause one board to lose its variant coding data, triggering the mismatch.

The primary corrective action is reflashing both the Operating Unit and the Power Unit with compatible, matched firmware. This process restores the variant coding on both boards simultaneously and ensures they are synchronized. Reflashing typically requires a Bosch service tool or diagnostic interface. Simply resetting the dryer by cycling power will not resolve this fault, as the coding mismatch persists in non-volatile memory until a proper firmware flash is performed.

Source: manufacturer service documentation.

Common causes of E:0120

  1. 01

    Replacement board with incorrect variant code

    Wiring / connection

    Installing a Power Unit or Operating Unit that carries a different variant code than the existing board will immediately trigger this error. The replacement part must be coded to match the specific dryer configuration.

  2. 02

    Interrupted or incomplete firmware update

    Wiring / connection

    If a firmware flashing procedure was interrupted by a power loss or connection failure, one board may have received updated coding while the other did not, causing a mismatch.

  3. 03

    Corrupted variant coding due to power surge

    Wiring / connection

    A voltage spike or power surge can corrupt the non-volatile memory on the Power Unit or Operating Unit, causing it to lose or alter its stored variant code.

  4. 04

    Faulty Power Unit with lost coding

    Part replacement

    In some cases the Power Unit board fails internally and loses its variant coding data entirely. If reflashing does not restore normal operation, the Power Unit itself may need replacement.

  5. 05

    Faulty Operating Unit with lost coding

    Part replacement

    The Operating Unit can similarly suffer memory failure that prevents it from holding a valid variant code. If the board cannot accept or retain a reflash, replacement of the Operating Unit may be necessary.

See the test procedure for each cause

Frequently asked questions about E:0120

What does E:0120 mean on a Bosch dryer?
E:0120 indicates a variant coding error between the Power Unit and the Operating Unit, the two main control boards in the dryer. These boards use embedded software identifiers to confirm compatibility with each other, and when those identifiers do not match, the dryer shuts down and displays this fault. It is the 4-digit form of the shorter code E:67. Reflashing both control units with matched firmware is the required fix.
Will resetting my Bosch dryer clear the E:0120 error?
No, a standard power reset will not clear E:0120. The variant coding mismatch is stored in non-volatile memory on the control boards, so it persists even after the dryer is unplugged and restarted. The error can only be resolved by performing a firmware flash on both the Operating Unit and the Power Unit using a compatible Bosch service tool.
How do I fix error code E:0120 on a Bosch dryer?
The required fix is to reflash both the Operating Unit and the Power Unit with compatible, synchronized firmware. This procedure requires a Bosch diagnostic tool and is not something that can be completed without the appropriate service equipment. A qualified appliance technician with access to Bosch service tools should perform this repair. If reflashing fails to resolve the error, one or both control boards may need to be replaced.
Is it safe to use my Bosch dryer when E:0120 is displayed?
The dryer will not operate normally when E:0120 is active because the control boards cannot communicate properly to manage heating and motor functions. Attempting to bypass or ignore this fault is not advisable, as the dryer requires both control units to be in agreement before it can safely run a cycle. The unit should remain out of service until the variant coding issue is corrected.
How much does it cost to repair a Bosch dryer with error code E:0120?
If the issue only requires reflashing the existing control boards, repair costs typically cover a service call and technician labor, generally ranging from around $100 to $250 depending on your location and the service provider. If one or both control boards have failed and need physical replacement, total repair costs including parts and labor can range from $200 to $500 or more. Getting a diagnostic estimate before authorizing parts replacement is recommended.

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