Display shows E7 and the mower will not start; often associated with wheel issues.

Safety first: Turn the mower OFF and wear gloves before working near wheels.

• Inspect wheels: Check both rear drive wheels for stones, branches, or packed grass between the wheel and chassis. Remove any obstructions.
• Spin wheels by hand: Lift the mower slightly and rotate each drive wheel. They should turn smoothly with some gearbox resistance but no grinding or tight spots.
• Check for damage: Look for cracked wheel hubs or missing tread lugs that could cause slipping and overload.
• Test on flat ground: Move the mower to a flat, dry area and start a manual mowing cycle. Observe whether one wheel struggles or stalls.

If one wheel remains stiff or noisy, the drive motor/gearbox assembly on that side is likely failing and should be replaced as a unit using genuine Stihl parts.