How to diagnose and solve pedal sensor problems on an electric bike

An electric bike's assistance system works thanks to the motor and battery that supply it with energy, but only if triggered by the rider's pedaling. The EAB must therefore detect when you start pedaling, via one or more sensors, of which there are several types.

A problem with one or more of the sensors can disrupt the electric assistance or even prevent it from working after a shock, in the presence of dirt or in the event of a breakdown. We explain the basics of pedaling sensor operation, the causes of malfunctions, and how to solve and prevent them.

The pedaling sensor sends electronic information to the electric bike's assistance system, enabling it to deliver the right power at the right time. An algorithm defines the level of assistance in real time, and when to cut off beyond the 25 km/h limit.

A distinction must also be made between different types of sensors:

• The cadence sensor provides information on crankset rotation speed (in rpm);
• The speed sensor sends the bike's speed data (in km/h), sometimes visible with a magnet/receiver duo on the rear wheel, or integrated into the rear motor;
• The torque sensor (Nm or Newton-meter) found on some bikes, notably those with Bosch, Shimano Steps or Yamaha central motors, detects the force of the foot on the crankset.
• The power sensor (W or watt) beloved by road cyclists, for precise performance measurement. They are installed in pedals, cranks, bottom bracket spiders or hubs.

The rotation sensor is a simple element. A magnet and its receiver detect the movement of the wheel, hence the delay at start-up between the start of pedaling and the activation of electric assistance.

On an electric bike with a rotation sensor, the rotation sensor plays the role of activating or deactivating the assistance. The latter will be at its maximum, i.e. send you to 25 km/h, if you start pedaling, no matter how hard you pedal.

We're talking here about rotation and torque sensors. The signs of a pedaling sensor problem are obvious:

• The motor does not activate,
• The electric bike's assistance is intermittent,
• This is usually a non-functional assistance system, operating intermittently or in fits and starts.

A faulty sensor is sometimes accompanied by an electric bike error code. Please refer to the owner's manual for your model, such as the Brose Drive S Mag, if you own such a motor.

To diagnose a pedaling sensor, the electric bike's display is the easiest and most accessible way. A Nakamura electric bike error code is specific to a given problem on an Intersport brand motor. However, the display of an error code is not systematic:

• In the case of a speed sensor (rotation), check whether the speed sensor magnet on one of the rear wheel spokes is still present or has moved,
• Observe whether a cable connecting the sensor to the controller is damaged or cut,
• If you have a torque sensor, detection is difficult because it's built into the crankset.

If there are no obvious visual elements, the problem requires the eye of an expert, as it may be electrical or electronic in nature (e.g. connection to the controller or false contact). You'll need a diagnostic tool or a repairer, if possible a partner of your engine brand.

For example, if you have a Bosch-assisted Moustache electric bike, the inspection will require the Bosch eBike Diagnostic Tool, or the Bafang BBS02 diagnostic guide for a Bafang electric bike.

With the exception of the position of a speed sensor magnet, or dirt interfering with the operation of a power sensor, any repair or adjustment should be carried out by a specialist.

However, it's a good idea to maintain your electric bike by cleaning it regularly. This includes regularly cleaning the speed sensor and checking its position, without waiting for your assistance to run into problems.

Each type of sensor has its own special requirements. In the case of a speed sensor, the magnet is easy to replace. Unscrew the defective magnet and screw the new one back in place, aligned with the receiver on the electric bike frame.

Torque - or power - transducers often come in tube - or hub - format, installed in the crankset axle. They are also specific to a particular brand or model of electric bike motor.

Because of the complex electrical connections, disassembly and replacement require expert intervention. Please contact a repair shop or partner center of your motor brand, for example Yamaha Customer Service if you own a Yamaha-assisted EAB.

Prevention is better than cure, which is a waste of time and money. Make sure you clean your bike often, and check that no parts, cables or components have been moved, damaged or are missing. In this way, you can keep an eye on your electric bike's components - brakes, transmission and speed sensor - and make sure it's working at its best.