When an electric bike powers up but stays still, check brake cutoffs, battery voltage, speed sensor, and controller connections first.
What This Symptom Tells You
Power reaches the display and lights, yet the motor does not drive. That points to a safety interlock, a sensor error, a low battery state, a loose connector, or a failed part. Start with the fast checks, then work toward signal tests. This order saves time and keeps you from chasing rare faults too early.
Fast Checks Before You Grab Tools
These quick wins catch many cases. Work down the list, then ride a short stretch to confirm.
- Release both brake levers and make sure lever travel is free.
- Spin the rear wheel and look for the speed magnet passing the sensor head.
- Set assist to a mid level and try walk assist if fitted.
- Cycle power off and on, then reseat the battery until it clicks home.
- Inspect the display for any error text or numeric code.
Common Causes And Quick Tests
The table gives a broad map from symptom to likely cause and a quick way to verify. Use it as your first pass.
| Symptom | Likely Cause | Quick Check |
|---|---|---|
| No assist, walk works for a moment | Brake sensor stuck, or controller fault | Unplug brake cutoffs and retry; if assist returns, replace the sticky switch |
| No throttle or pedal assist | Brake cutoff latched or low voltage cut | Disconnect cutoff leads; charge battery to full and test on a stand |
| Display on, motor silent | Loose hall, PAS, or throttle plug | Check arrows on waterproof plugs; reseat until fully keyed |
| Works then cuts out on hills | Voltage sag past controller limit | Read pack voltage at rest, then under load; swap in a known good pack |
| Assist dead after washing | Moisture inside connectors or motor | Dry all plugs, leave bike in a warm, dry room, then retest |
| Speed shows zero while moving | Speed sensor gap or magnet misaligned | Align magnet with sensor mark; set a 2–5 mm gap |
| Intermittent surging | Torque or cadence pickup misread | Clean sensor faces; check pickup clearance set by the maker |
Brake Cutoffs Can Hold The Motor Off
Most setups route tiny reed or hall switches inside the levers. If a lever sticks, or a magnet drifts, the controller reads “braking” and refuses to drive. Pull the two small cutoff plugs from the controller harness, then test in a safe area. If assist returns, replace the lever switch or adjust the tiny magnet. Keep the bike secure on a stand while testing any live wiring.
Battery State And Low-Voltage Cut Behavior
Many no-drive cases trace to a pack that sags under load. Two guardians protect cells: a display or controller limit, and the pack’s battery management board. The controller watches total pack volts and stops drive below a set floor. The pack board watches each cell group and can trip earlier. When the pack board trips, you often need a power cycle or a charger bump to clear the trip. Charge fully, then test on flat ground before blaming sensors.
Speed Sensor Alignment Is A Small Thing With A Big Effect
Drive units need a valid wheel speed to run. A sensor that sits too far from the magnet can block all assist. Rotate the wheel and watch the display speed readout. If it stays at zero, move the magnet to line up with the mark on the pickup, set a paper-thin gap, and retest. Many brand error codes point at this exact issue.
Brand Error Codes And Where To Look Them Up
Many displays show a short code that points to the fault area. That code saves time. Check your brand’s list for the meaning and steps. For mid-drives from a well known maker, use the official pages that index codes. See the pages that list Shimano error and warning codes and the Bosch help entry for walk assist to see how brands describe common no-assist cases and the resets that clear them.
Step-By-Step Diagnostic Flow
1) Confirm Battery Health
- Charge to full until the charger light changes state.
- Measure open-circuit volts at the discharge port with a meter suited to DC.
- Ride a short climb and watch for steep drop under load. A drop that kills drive points to a tired pack or a high current draw.
- Try a second pack if you have one. A swap makes the call in minutes.
2) Clear Cutoffs And Interlocks
- Unplug both brake cutoff leads from the harness.
- On models with a kickstand switch, flip the stand up and check the switch action.
- Reset walk assist and test ride on low assist in a clear area.
3) Verify Speed Signal
- Line up the wheel magnet with the sensor mark.
- Set the gap to a few millimeters and tighten the spoke mount.
- Spin the wheel and confirm the display speed rises.
4) Inspect Connectors, Then Harness
- Power down and pull the main waterproof plugs one by one.
- Check for bent pins, green corrosion, or loose locking tabs.
- Match the arrows and push until the joint seats fully.
- Wiggle test the harness while the bike is on a stand to catch breaks under the jacket.
5) Check The Sensors That Tell The Controller To Drive
- For a cadence ring, confirm the gap to the pickup and that the ring spins true.
- For a torque unit, keep the crank bolts to spec and redo any brand-specific zeroing steps listed on the maker page.
- For a thumb or twist throttle, read the signal at the controller plug with a safe meter lead. A dead flat signal points to a bad hall sensor in the throttle.
6) Read The Code And Follow The Official Tree
Once the basics are clear, pull the code screen and follow the brand tree. Code pages list exact checks for speed pickups, torque zero, over-current trips, and more. If the tree calls for dealer software, book a bench test. That saves parts swaps.
Hub Motors Versus Mid-Drives
Hub Systems
- Common faults: bent pins in the axle plug, damaged phase leads, bad hall set in the hub.
- Tell-tale signs: rough push feel with power off, motor jerks when lifting the wheel and blipping throttle.
- Quick check: unplug the hall lead and try sensorless start if your controller allows it; if it runs rough, halls may be gone.
Mid-Drive Systems
- Common faults: torque pickup drift, speed sensor gap, water ingress at motor seams.
- Tell-tale signs: walk assist works briefly, then quits; assist pulses; speed reads zero with the wheel turning.
- Quick check: realign speed magnet, redo torque zero per brand notes, then retry on low assist.
Water And Corrosion Are Quiet Motor Killers
Spray from rides and wash sessions creeps into plugs and housings. That raises resistance and throws off tiny sensor signals. Dry the bike, use contact cleaner on low-voltage plugs, and avoid high-pressure spray near the motor or harness. If the bike sat after a wet ride, open plugs and let the pins air dry before your next test.
When Low Voltage Stops Drive
Every system sets a floor for safe pack volts. Common pack sizes share rough cut points based on cell chemistry. The exact value lives in your display or pack board, yet the ranges below help frame tests.
| Pack Label | Cells In Series | Typical Cut Floor* |
|---|---|---|
| 36 V | 10s | ~31–32 V controller cut; BMS may trip earlier |
| 48 V | 13s | ~41–42 V controller cut; BMS may trip earlier |
| 52 V | 14s | ~44–46 V controller cut; BMS may trip earlier |
*Ranges based on common kit settings and maker notes; cell group trips from the pack board can occur at higher pack volts when a weak group sags.
Controller, Motor, Or Harness Faults
After clearing the basics, stubborn no-drive points to a failed board, a broken hall set inside the motor, or a harness break. Hall failures often show as cogging, a rough feel when you push the bike with power off. A shorted phase wire can blow a fuse inside a controller. Harness faults show up when moving bars changes the fault. A dealer with brand software can run hall and phase tests in minutes.
Throttle-Only Bikes: Extra Checks
- Make sure the display allows throttle at zero speed; some settings block it until a pedal rotation.
- Check for a tight return spring in the throttle housing.
- Probe signal and ground at the controller side; a flat line suggests a failed hall chip in the throttle.
After Storage Or Shipping
- Look for crushed sections of the harness near the head tube and under the downtube.
- Clean and reseat every waterproof plug; tape labels so they do not pull under bar rotation.
- Charge the pack slowly if it sat for months; some boards need a wake pulse from the charger before they pass current.
Tools And Supplies That Help
- Bike stand that holds the rear wheel off the ground.
- Digital multimeter with sharp probes and DC range suited to your pack.
- Isopropyl alcohol and contact cleaner for low-voltage connectors.
- Zip ties and dielectric grease for harness strain relief and moisture resistance.
- Torque wrench for crank and sensor mounts on mid-drives.
Pro Tips For Reliable Assist
- Seat the battery with a clean, dry interface; keep contacts bright.
- Keep the speed magnet aligned with the sensor mark and maintain a tight gap.
- Route harness loops with gentle bends; avoid tight kinks at the head tube.
- Skip pressure washing near the motor; hand rinse and dry plugs after wet rides.
- Update brand firmware during shop visits when the display offers a clear prompt.
Simple Fixes That Close Many Tickets
- Reseat the battery and clean the pads.
- Realign the speed sensor magnet and set a tight gap.
- Unplug sticky brake cutoffs and replace the weak lever switch.
- Dry every plug after wet rides and avoid pressure washing.
- Charge the pack to full and retest on flat paths.
When To See A Dealer
Go in when the code requires software steps, when the pack trips on light loads, or when the motor cogs with power off. Bring your charger, battery, and the code notes. A clean list of steps already tried speeds the bench test.
Printable Quick Start Checklist
Power And Pack
- Charge to full and reseat the battery.
- Read open-circuit volts, then a short hill under load.
Cutoffs And Sensors
- Unplug brake cutoffs; test speed pickup alignment.
- Set PAS ring gap and secure bolts.
Harness And Controls
- Inspect and seat all waterproof plugs.
- Test throttle signal at the plug if fitted.
Error Codes
- Note the code and match it on the brand list.
- Do resets listed by the maker, then road test.