What Error 550 Means

Error 550 signals that the drive unit current monitoring circuit has detected an abnormal load — the motor is drawing significantly more current than expected for the detected speed and torque input. This indicates a mechanical resistance in the drivetrain or motor forcing it to work harder than normal.

Common Causes

  1. Dragging brake caliper — A partially engaged brake pad creates substantial constant drag the motor compensates for until excess current trips error 550.
  2. Chain wear or binding — A stiff link or extreme drivetrain misalignment creates resistance spikes.
  3. Seized bottom bracket — A failed BB bearing creates significant rotational resistance.
  4. Motor bearing degradation — Internal bearing wear increases motor rotational friction.

Diagnosis Procedure

Step 1: Check Brakes

Lift the rear wheel and spin by hand. It should rotate freely for several revolutions. If it stops quickly or you hear rubbing, a brake caliper is dragging.

Step 2: Inspect the Drivetrain

Pedal the bike backwards by hand and listen for grinding or clicking. Flex each chain link section — stiff links are visible as kinks in the chain line.

Step 3: Check the Bottom Bracket

Remove the cranks and spin the BB spindle by hand. It should rotate smoothly with no grinding.

Step 4: Motor Bearing Inspection

If all external drivetrain components check out, listen for grinding from the motor housing during operation. Motor bearing replacement requires a Bosch-certified dealer.