Quick answer: when an electric bike conversion kit stops working, begin with the safest, simplest checks: stop riding, switch the system off, remove the battery if the manufacturer permits, inspect the display message, confirm the battery is seated, and look for loose, wet, damaged or incorrectly matched connectors. Do not open a battery pack or probe live high-current wiring unless you are trained and equipped to do so.
Most faults fall into a few groups: no system power, motor assistance missing, intermittent pedal assist, controller or display error codes, battery cut-outs under load, brake cut-off problems, or mechanical wheel and spoke issues. This guide helps you narrow the symptom and gather useful information for the retailer, installer or manufacturer.
Conversion-kit fault finder at a glance
| Symptom | Common areas to check | Safe first action |
|---|---|---|
| Display will not switch on | Battery charge and seating, key/switch, display cable, main harness, fuse only if externally serviceable | Power off, reseat approved connectors and try the correct charger/status check |
| Display works but motor does not assist | Assist level, brake cut-offs, PAS sensor, throttle state, speed sensor, motor cable, error code | Return controls to neutral, inspect sensors and record the code |
| Pedal assist starts and stops | PAS disc alignment, sensor gap, crank movement, loose connector, brake lever switch | Inspect the magnet ring and cable without turning the system on |
| Power cuts out on hills | Battery state of charge, voltage sag, BMS current, controller demand, hot connectors or controller | Stop loading the system and let components cool in a safe location |
| Motor judders or makes harsh noise | Motor phase/hall connection, damaged cable, loose axle, wheel/spokes, internal motor fault | Stop riding and check wheel security mechanically |
| Error code on display | Code varies by display, motor and firmware | Photograph the exact code and use the correct manufacturer manual |
| Wheel rubs, wobbles or spokes ping | Wheel seating, dish, spoke tension, tyre, brake rotor, axle nuts and torque arms | Do not ride until the wheel is secure and true |
Start with a safe power-down and visual inspection
- Stop in a safe place and switch the display and battery off.
- Remove the battery only in the way described by its manufacturer. Do not force a jammed pack.
- Wait for moving parts to stop. Keep fingers, clothing and tools away from the chain, chainring and wheel.
- Look and smell for heat damage, melted plastic, corrosion, water, pinched cables, cuts, crushed insulation or loose axle hardware.
- Photograph the display, connector positions and any damage before disconnecting anything.
- Check one item at a time so you know which change affected the fault.
Never connect or disconnect a motor, display, PAS sensor or controller harness while the system is powered unless the manufacturer explicitly requires that procedure. Never bridge pins, bypass a fuse, defeat a battery management system or use a charger simply because its plug fits.
1. The display will not switch on
A completely blank display usually points to the power path rather than the motor itself. Confirm that the battery is the correct voltage for the kit, has been charged with its authorised charger and is fully latched into the mount. Check any battery key or external on/off switch.
Inspect the main battery-to-controller connector and the display/harness connection while the battery is disconnected. Waterproof circular connectors often have alignment marks; forcing them can bend pins or damage seals. Push only on the connector body, never pull the cable.
If the battery charge indicator behaves abnormally, the charger never completes its normal sequence, or the pack has suffered a drop or crash, stop using it and contact the supplier. Do not open the case to test individual cells.
2. The display works but the motor will not assist
Check the selected assist level first; level zero can leave the display on while providing no motor support. Make sure a brake lever is not partly applied and that each brake cut-off sensor returns fully. A displaced magnet on an add-on hydraulic brake sensor can keep the controller in a permanent “braking” state.
Next inspect the pedal-assist sensor, speed sensor and motor cable. Record any display code before restarting the system. If walk assist or throttle behaviour differs from pedal assist, that distinction can help a technician identify whether the fault lies with the PAS input, brake input, control harness or motor path.
3. Pedal assist is intermittent or delayed
A split magnet disc or PAS ring must sit in the correct orientation and pass the sensor at the specified gap. If it has moved sideways on the crank spindle, the controller may receive an uneven signal. Look for a loose retaining ring, missing magnets, a cracked disc or a sensor bracket that has rotated.
Do not assume every PAS sensor uses the same direction or pin arrangement. Replacing it with a visually similar part can damage the controller if voltage, signal or connector pinout differs. Match the exact model or obtain written compatibility confirmation.
If assist cuts out when the handlebar turns or the frame flexes, inspect cable routing for excessive tension, pinch points and intermittent connectors. Leave enough service loop at the handlebar while keeping cables away from tyres, chainrings and sharp edges.
4. Throttle or walk assist does not work
Some controllers disable the throttle in certain modes, after a brake input, when an error is active or when the throttle is not at its neutral position during start-up. Switch off, return the throttle fully to rest, release the brakes and restart only after checking the manual.
Throttle rules and functions vary. Do not alter settings to bypass UK road-use requirements. See our UK e-bike law and throttle guide for the classification issues that apply to the completed bicycle.
5. How to handle controller and display error codes
Error codes are not universal. The same number can mean different things on different displays, protocols or firmware versions. Write down the full display model, motor model, controller label and exact code, then use the matching manual.
Bafang's official service FAQ lists examples including throttle position, over-voltage, hall sensor, motor phase, temperature, speed sensor, torque signal, controller current and communication faults. Its separate speed-sensor fault procedure shows why model-specific instructions matter: it asks for sensor alignment, clearance and connector checks in a defined order.
Use these examples only for compatible Bafang systems. For another kit, use that manufacturer's documentation rather than translating a Bafang code table across brands.
6. The battery cuts out under load
A kit that powers up normally but shuts down on a hill or under acceleration may be experiencing low charge, voltage sag, battery-management protection, excessive controller demand, a weak connection or overheating. Let the system cool and do not repeatedly force it to restart.
Confirm that the battery nominal voltage matches the controller and that the battery-management system supports the controller's maximum current. Capacity in amp-hours or watt-hours does not by itself prove sufficient discharge capability. Read our 36V, 48V and 52V battery guide before replacing a pack.
A connector that becomes hot, discoloured or soft requires professional attention. Do not improve contact by squeezing pins, adding foil, bypassing a connector or soldering near an installed battery.
7. Motor judder, vibration or harsh noise
Stop riding if the motor jerks, growls, stalls or produces a new grinding sound. Check first for mechanical causes: loose axle nuts, a displaced torque arm, tyre or rotor rub, loose spokes, a damaged rim or a cable touching the wheel.
Electrical causes can include motor phase or hall-sensor faults, a damaged motor cable at the axle, poor connector contact or an internal controller/motor problem. These checks can require electrical expertise and model-specific equipment. Do not continue applying throttle to a stalled motor; high current can rapidly heat the controller, wiring and windings.
8. Wheel wobble, loose spokes or axle movement
A hub motor wheel adds mass and torque at the wheel. Check that the axle sits fully in both dropouts, anti-rotation washers and torque arms are correctly positioned, and fasteners are tightened to the manufacturer's specification. Do not copy a torque value from an unrelated kit.
Listen for spoke pings, inspect for visibly loose or broken spokes and watch the rim relative to the brake or frame while turning it by hand with the battery removed. Randomly tightening individual spokes can worsen dish and tension balance; a motor wheel with recurring spoke problems should be assessed by an experienced wheel builder.
If the axle has rotated in a dropout, stop using the bicycle. The frame or fork, motor cable and retention hardware may all be damaged.
9. Brake cut-off faults
If the motor never starts, disconnecting a brake sensor may be used as a diagnostic step only when the manufacturer's manual permits it and the bicycle is secured for a controlled workshop test. Never ride with required brake cut-offs disabled.
If the motor continues when braking, stop riding immediately. Check lever return, sensor/magnet alignment and the brake-harness connector. A “runaway” or delayed cut-off condition requires professional diagnosis before further use.
10. Water, corrosion and damaged connectors
Water-resistant does not mean waterproof under every condition. After heavy rain, washing or storage in damp conditions, switch off and inspect connector seals and low points in the cable run. Do not use a pressure washer, heat gun or compressed air on electrical components.
Green or white corrosion, bent pins, cracked housings or missing seals require the correct replacement connector or harness. Mixing connector families that look similar can reverse polarity or place voltage on a signal pin.
What not to do when troubleshooting
- Do not open, puncture, crush or modify a lithium-ion battery.
- Do not use an unapproved charger or adapter.
- Do not bypass the BMS, fuse, brake cut-off or controller protection.
- Do not test a motor by holding the wheel off the ground with an unsecured bicycle.
- Do not keep restarting a system that cuts out, overheats or smells unusual.
- Do not replace components on connector shape alone.
- Do not ride with a loose motor axle, damaged cable, unreliable brakes or wheel wobble.
Information to collect before contacting support
- Order number and installation date
- Motor, controller, display, battery and charger model labels
- Battery voltage and controller current rating
- Exact error code and when it appears
- Whether display, pedal assist, throttle and walk assist work independently
- Conditions when the fault occurs: cold start, hill, braking, bumps, rain or handlebar movement
- Clear photos of connectors, axle/dropouts, PAS sensor and display
- Any recent crash, battery drop, water exposure, setting change or component replacement
This record helps support distinguish compatibility, installation, mechanical and component faults without asking you to repeat unsafe tests.
Choose compatible replacement parts
Before ordering a replacement controller, display, PAS sensor, battery or harness, match the complete specification and connector pinout. Our conversion-kit compatibility checklist covers wheel, frame, brake, electrical and battery fit.
Browse e-bike accessories and spare parts for compatible components, or compare complete electric bike conversion kits when several parts are damaged or mismatched. Professional installation is recommended where appropriate.
Conversion-kit troubleshooting FAQs
Why does my e-bike display turn on but the motor not work?
Common areas include assist level zero, an active brake cut-off, PAS or speed-sensor alignment, a loose motor cable or an error code. Power down before inspecting connectors and use the correct manual for the display and controller.
Why does my conversion kit cut out on hills?
The battery may be low, sagging under load, reaching BMS protection, mismatched to controller current or overheating. A loose high-current connector or hot controller can also cause cut-outs. Stop loading the system and have hot or damaged parts assessed.
Can I reset an e-bike error code?
A restart may clear a temporary state, but recurring codes require the model-specific diagnostic procedure. Photograph the code first and do not repeatedly reset temperature, over-current or battery faults.
Can I use any PAS sensor or display with my controller?
No. Voltage, communication protocol, signal type, connector and pinout must match. Similar-looking parts are not proof of compatibility.
When should I take the bike to a professional?
Use professional help for battery damage, melted or hot connectors, axle/dropout movement, brake faults, recurring over-current or temperature codes, internal motor/controller faults, wheel building and any live electrical testing.
Safety and manufacturer sources
- GOV.UK: Battery safety for e-cycle users
- OPSS: Statutory lithium-ion battery safety guidelines
- Bafang: Error codes and common faults
- Bafang: Manuals and service downloads
Last reviewed: 9 August 2026. This guide provides general diagnostic information and does not replace the instructions for your exact kit or professional electrical and mechanical assessment.