When your Bosch washer flashes Er:09, it’s telling you the “brains” of the machine (the main control) and the “muscle manager” (the motor control) aren’t communicating reliably. That digital conversation powers everything from drum start-ups to spin-speed changes. If that link is shaky or dead, the washer can’t run as designed.

How this usually shows up

Most owners notice one or more of these: the drum won’t start, it jerks and stops, the cycle never ramps up to a proper spin, or the machine aborts mid-wash and posts Er:09. Sometimes you’ll hear a brief relay click, then nothing.

Why it happens

Nine times out of ten, the problem isn’t dramatic—it’s a wiring issue. Vibrations and heat cycles can loosen plugs or fatigue a section of the wire harness between the boards. Less commonly, the motor control module itself fails, and in rare cases the main control is the culprit.

A safe, sensible way to fix it

Start by unplugging the washer. Give it a minute to fully power down.

Now, think of the repair as restoring a clean signal path:

• Reconnect what’s loose. Open the control area and the base (where the motor lives). Reseat the multi-pin connectors on both the main control and the motor control. A connector that looks “mostly on” can still be the issue—push until it’s fully home.
• Trace the harness. Follow the cable that runs between the two boards. Look for pinched insulation, heat discoloration, greenish corrosion on pins, or spots where the wires have been rubbing against metal. If you see any of that, the harness has to go—replace it rather than trying to tape your way out of trouble.
• Re-test. After reseating connectors, plug the washer back in and start a short cycle. If Er:09 disappears and the drum spins up smoothly, you’ve likely fixed a loose connection.

If the error returns:

• Swap the harness. Communication errors love to hide inside the cable itself. A fresh harness often restores a clean signal.
• Evaluate the motor control module. If a new harness doesn’t help, the motor control board is the next most likely cause. A failing board can pass a quick check but drop out under load.
• Last resort: main control. Only after the harness and motor control have been addressed should you consider replacing the main control module.

When to call a pro

If you don’t have a multimeter, aren’t comfortable opening panels, or your washer shows repeated Er:09 after a harness replacement, it’s time for a technician. A pro can run continuity tests, check board voltages, and confirm whether the motor control or main board is failing—saving you from unnecessary parts swaps.

Bottom line

Er:09 is almost always a communication problem, not a mystery motor failure. Start with power off, reseat every connector, inspect and—if needed—replace the harness, then move on to the motor control module. With a clean signal path restored, your Bosch typically returns to normal wash and spin without drama.