What Error W012 Means

Error W012 on Yamaha PW series motors signals that the cadence sensor is not providing reliable pedal rotation data. The cadence sensor detects how fast you are pedalling — measured in RPM — and the motor uses this data alongside the torque sensor reading to calculate the appropriate level of assistance. Without reliable cadence data, the system cannot deliver smooth, proportional assistance and raises W012.

Unlike the speed sensor (W011), the cadence sensor on Yamaha PW motors is typically integrated into the motor housing and reads from a magnet ring on the crank spindle rather than a spoke-mounted magnet. This means the fix approach is different.

Common Causes

  1. Contaminated magnet ring — Metal debris from a worn chain or chainring can adhere to the cadence magnet ring inside the motor housing, disrupting the sensor reading.
  2. Damaged or worn magnet ring — High-mileage PW motors can develop micro-fractures in the cadence magnet ring, causing signal gaps at certain crank positions.
  3. Loose crank arm — A crank arm that has worked loose allows slight axial movement of the crank spindle, which moves the magnet ring out of optimal sensor range.
  4. Internal sensor failure — The Hall sensor reading the magnet ring has failed. This requires dealer repair.

Fix Procedure

Step 1: Power Cycle and Retest

Remove battery for 30 seconds. Reinstall and test. Error W012 caused by a single signal dropout (e.g., from a brief crank reversal or impact) often clears on restart.

Step 2: Check Crank Bolt Torque

Verify both crank arm pinch bolts are torqued to 12 to 14 Nm. A loose crank arm is a common cause of intermittent cadence sensor errors.

Step 3: Inspect Accessible Magnet Area

With the crank arms removed, look through the motor housing gap for any visible metal debris adhering to the inner components. A magnet cleaning tool or compressed air can clear fine metal particles from the magnet ring area without motor disassembly.

Step 4: Dealer Diagnosis

If W012 persists after the above steps, the Yamaha diagnostic tool is required to read the exact cadence sensor output and determine whether the magnet ring or the sensor element itself has failed. Both are internal motor components requiring dealer service.