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Error code reference

Bosch Washer Error Code Er:09

Communication lost to motor

Bosch codesBosch washer codes

Communication lost to motor — faulty wire harness.

First step from the service manual

Run test P4; check wire harness between control module and motor control.

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

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What Er:09 means on a Bosch washer

Er:09 on a Bosch washer indicates that the main control module has lost communication with the motor control unit. The washer relies on a continuous data connection between these two modules to coordinate motor speed, direction, and load sensing. When that communication link is interrupted or corrupted, the control module logs Er:09 and halts operation to prevent damage from uncontrolled or unmonitored motor behavior.

The most common root cause is a fault in the wire harness that runs between the main control board and the motor control module. This harness carries both power and signal lines, and any break, pinched wire, corroded connector, or loose terminal can drop the communication signal entirely. Vibration over time is a frequent contributor, as the harness flexes with each wash cycle and connection points can work loose or develop intermittent faults.

To begin diagnosis, run test P4 as directed by the diagnostic routine. This test exercises the motor communication pathway and helps isolate whether the fault is in the harness, the motor control module, or the main control board itself. Visually inspect the full length of the harness for chafing, pinched sections near cabinet edges, or burn marks at connectors. Check each connector for corrosion, bent pins, and secure seating before condemning either control module.

Source: manufacturer service documentation.

Common causes of Er:09

  1. 01

    Damaged or disconnected wire harness

    Part replacement

    The harness between the main control module and motor control module can develop breaks, loose connectors, or pinched wires from vibration and movement over time. Inspect the full harness run for visible damage and reseat all connectors firmly.

  2. 02

    Corroded or loose connector terminals

    Wiring / connection

    Moisture inside the cabinet can cause terminal corrosion at the harness connectors on either module, creating high resistance or an open circuit in the communication line. Check each connector for green or white oxidation and bent or recessed pins.

  3. 03

    Faulty motor control module

    Part replacement

    If the harness and connectors check out, the motor control module itself may have failed internally and is no longer responding to the main board. Test P4 can help confirm whether the module is the source of the communication failure.

  4. 04

    Failed main control board

    Part replacement

    Less commonly, the main control module loses the ability to transmit or receive communication signals due to a component failure on the board. This is typically diagnosed only after the harness and motor control module have been ruled out.

See the test procedure for each cause

Frequently asked questions about Er:09

What does Er:09 mean on a Bosch washer?
Er:09 means the main control module has lost communication with the motor control module. This communication link is required for the washer to operate the motor safely. The fault is most often caused by a problem in the wire harness connecting the two modules. The washer will stop and refuse to run until the communication is restored.
Can I fix Er:09 myself on a Bosch washer?
A knowledgeable DIYer can attempt the repair by inspecting and reseating the wire harness connectors between the main control board and the motor control module. If connectors are corroded or terminals are damaged, cleaning or replacing the harness may resolve the issue. If the harness is intact, the repair likely involves replacing a control module, which is more involved but still possible with basic appliance repair skills.
Will resetting my Bosch washer clear the Er:09 error?
A power reset may temporarily clear the error display, but if the underlying wiring or component fault is still present, the code will return as soon as the washer attempts to run the motor. A reset is not a fix for Er:09. The root cause in the harness or control modules must be addressed for the washer to operate reliably.
Is it safe to use my Bosch washer when it shows Er:09?
No. When Er:09 is active, the washer halts operation because the control system cannot reliably monitor or control the motor. Continuing to force the machine to run without resolving the communication fault could result in motor damage or erratic operation. Do not attempt to bypass the error.
How much does it cost to repair Er:09 on a Bosch washer?
If only the wire harness needs replacement, repair costs typically range from around $50 to $150 including parts and labor. If a motor control module or main control board needs to be replaced, costs can rise to the $200 to $450 range depending on the specific parts required and local labor rates. Getting a diagnostic run first helps avoid replacing parts unnecessarily.

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