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Husqvarna Automower error 18

Collision sensor problem, rear

Also shown as E18 · fault code 18 · message 18

The rear collision sensor has been activated. The direction is the useful part: a fault that is always at the rear points at that end of the machine — what it reverses into, or what has worked its way into the body-to-chassis gap back there — rather than at the sensors as a whole.

Common causes

• Debris lodged between the body and the chassis, which the sensors read as a permanent collision.
• The mower body not fully seated, or dirt stopping it moving freely on its mounts.
• The mower physically stuck against something it can't reverse away from — under garden furniture is the classic one.
• Grass taller than the model is rated for, or a cutting height set too low, so the mower is constantly loading against the turf.
• A blocked drive wheel.
• A temporary electronic or firmware problem.

How to fix it

1. Look in the gap between the body and the chassis and brush out any grass, twigs or dirt. This is the most common cause and costs nothing to rule out.
2. Check the body is fully in place and moves freely on its mounts — that movement is what the sensors measure, so anything binding it reads as a collision.
3. Make sure the mower isn't wedged against something. Free it and let it reverse away.
4. Cut long grass down with a conventional mower first, and raise the cutting height if it is set low — both leave the mower pushing against more resistance than the sensors expect.
5. Check both drive wheels turn freely and nothing is wound around them.
6. Restart the mower. If the app offers “Reset Error”, use that and then restart from the app.
7. If it comes back after all of that, it is a dealer job rather than something to keep clearing.

Related codes — Collision & bump sensors

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