When an e-bike stops working, the expensive guess is to replace the motor or the controller first. Most faults can be narrowed down with checks that cost nothing: a plug that has worked loose, a brake lever that is not returning, a battery that is not fully seated. This page is the starting point for our repair guides. It tells you what to check, in what order, and where to go next for each symptom.
The rule: free checks before parts
Our free e-bike diagnosis asks what the bike is doing and walks you through the checks for that symptom in a fixed order, from the most likely and cheapest cause to the least likely. Parts come after the free checks, not before. If you prefer to work through it yourself, the steps below follow the same idea. Our how we diagnose page explains the method.
Before any check
- Turn the bike off and remove the battery before you unplug, inspect or reseat any connector. Pulling a plug under power can spark and damage the electronics.
- Charge the battery fully and refit it until it clicks or locks. Many apparent faults are a low or badly seated battery.
- Write down what happens: what the display shows, any error code, and when the problem started. A photo of the display and of any plug you open helps later.
Find your symptom
- Nothing turns on. Work along the power chain: battery switch and charge, battery contacts and fuse, the main plug, then the display. Our power chain checklist takes you through it.
- Battery is fine but the display stays dark. Reseat the display plug, look for bent or corroded pins, and hold the power button a few seconds. See display won't light up.
- Display works but there is no assist. Check the brake levers first: a brake cutoff sensor stuck on tells the motor to stay off. Read the brake sensor guide, then pedal assist not working.
- Throttle does nothing but pedal assist works. Check the throttle plug and the display settings, then test the throttle with a meter: throttle test in 10 minutes.
- Motor shudders, grinds or will not spin. Inspect the motor plug for water or pushed-back pins, check the axle nuts are tight, then test the Hall sensors and phase wires: Hall sensor and phase wires and the phase and Hall combination guide.
- The display shows an error code. Photograph it and look it up in the shared 21 to 30 code family or your brand's code list. Reseat every plug before replacing anything.
- It cuts out while riding. Note when it happens: on hills, over bumps or at low charge. Check the battery contacts and latch, then read battery sag or controller.
- The motor runs by itself. Stop riding, turn the bike off and remove the battery, then read motor runs by itself before powering it again.
When you need a meter
A basic multimeter set to DC volts answers most of the questions the free checks leave open: is the battery delivering voltage, is the throttle signal changing, are the Hall sensors switching. Our five multimeter measurements explains each test. Make sure the meter's DC range is above your battery's full-charge voltage before you touch the probes.
If you have more than one fault, or the checks give mixed results, the minimal system method strips the bike down to the parts it needs to run and adds the rest back one at a time.
Battery safety
- Never open a battery case or try to repair cells yourself. Bosch's manual tells owners not to open any of the system's components and to leave service to an authorized dealer.
- Keep the battery terminals away from keys, coins and tools. A short circuit can deliver a very high current.
- If a battery is swollen, unusually hot, smells, or has been under water, stop using it, do not charge it, and keep it outdoors away from anything that can burn.
Found the faulty part? Use find my part to match a replacement to your bike.