When an e-bike's display lights up but the motor will not drive, power is at least reaching the display. That narrows the search to the parts that can hold the motor off or fail to ask it for power: the brake cut-off, the display settings, the throttle and pedal-assist sensor, the low-voltage supply those sensors share, the motor cable and its Hall signals, and last, the controller. This page puts those checks in the order that costs least. If nothing lights up at all, go to the second section.
What you see, and where to look first
| What you see | Most likely link | First free check | Read |
|---|---|---|---|
| Brake icon on the display, or no drive and no code | A brake cut-off reporting "applied" | Squeeze and release both levers; watch each blade return fully. Check nothing on the bar rests against a lever. | Brake sensor guide |
| A code on the display | The circuit the code names | Find your display's code system before you trust a table. | E-bike error codes |
| Throttle drives, pedalling does nothing | The pedal-assist chain | Assist level above zero, sensor plug seated, gap between sensor and magnet ring. | Pedal assist: 5 fixes |
| Pedal assist works, throttle does nothing | The throttle, or a setting that limits it | Some displays have a setting that disables the throttle or limits when it works. Check the menu, then measure the throttle's supply and signal. | Throttle test in 10 minutes |
| Neither throttle nor assist, no code | Brake cut-off first, then the shared low-voltage supply and what reaches the controller | Brake check; after a new controller, its enable (key) wire. | Key switch wire |
| Motor hums, judders or twitches but will not turn | Motor plug, Hall signals, or phase and Hall wire order | Battery out, open the motor connector, look for water, corrosion or bent pins. | Hall sensor test |
| Stopped after rain or washing | Water in a connector | Battery out, separate the plugs, dry and inspect them. | Water in the motor connector |
| Nothing after fitting a new controller or kit | A missed connection, or a controller and display that do not match | Compare every plug with your photos; check the enable wire and the display model. | Controller replacement |
The order, as a decision path
- Is there a code? Yes: write it down with the display model and go to error codes; a code names a circuit, so check that circuit's connector before you buy any part. No code: carry on here. Many brake and throttle faults show no code at all.
- Rule out the brake cut-off. Work both levers through their travel and let them snap back. Then switch off and remove the battery, unplug one brake sensor, refit the battery, lift the driven wheel and try the throttle. If the motor wakes, you have found the side. Unplugging is only a quick test and does not behave the same way on every bike, so no change does not clear the sensors; the brake sensor guide has the meter test. Battery out again before you plug it back in, and never ride with a sensor unplugged.
- Check the settings. Assist level above zero, the throttle not disabled in the display menu, and no mode that limits it. If the throttle does nothing at assist level 0, try it at level 1 with the wheel lifted before you suspect the part.
- Split the problem with the throttle. With the wheel lifted, try the throttle. If it drives the motor, the controller can run the motor, and the fault most likely sits in the pedal-assist chain: see cadence sensor troubleshooting. If pedal assist works and only the throttle is dead, measure the throttle with the bike switched on, back-probing its plug: first its low-voltage supply against ground (Grin Technologies' throttle test guide expects roughly 4 to 5 V), then the signal as you move the throttle slowly through its travel. Supply present but a signal that never moves, or one that jumps and drops out, points at the throttle. A missing or low supply does not clear the throttle on its own: the cause can be the plug, a broken supply or ground wire, the controller, or a part on the same low-voltage line pulling it down, and that includes the throttle itself. See the throttle test, and isolate the supply as in step 6.
- Neither works? Listen at the motor. A hum, judder or twitch shows that power is reaching the motor: battery out, inspect the motor connector, then test the Hall sensors. If phase and Hall wires were reconnected recently, the order may be wrong; the 36-combination method works through it with the power off for every change. Complete silence does not clear the motor. On many bikes the throttle, the pedal-assist sensor and the Hall sensors inside the motor run from one shared low-voltage supply, and a short in any one of them can pull that supply down, so neither the throttle nor pedal assist can work. Step 6 checks it.
- Measure the supplies before you buy anything. First, battery voltage at the controller's input, with the meter on a DC volts range above your pack's voltage. If there is none, confirm the battery itself is switched on and giving its voltage, since a pack's own protection can switch it off (the second section covers this); once the pack is confirmed, no voltage at the controller means a plug, fuse or cable between the two. Second, the low-voltage supply on a throttle or Hall plug against ground, back-probed with the bike on (often around 5 V; confirm your own system's figure). If it is missing or well below that, do not order a controller or a motor yet. Switch off and remove the battery, unplug the throttle, refit the battery and measure again at a plug that is still connected; repeat for the pedal-assist sensor and then the motor's sensor plug, battery out before every unplug and reconnect. If the supply comes back with one part unplugged, that part or its cable is the likely cause. Pedego's dealer service guide isolates a shorted 5 V circuit the same way, one part at a time. If you are not sure how to do this on your bike, follow your controller's manual or the Hall sensor test, which walks through the readings.
- Only then suspect the controller. Battery voltage at its input, a healthy low-voltage supply, a throttle signal that moves and brakes reading released, but still no drive: now the controller is the prime suspect. The controller, display or both guide is the next step.
Change one thing at a time and test after each change, so you know which one mattered. If nothing obvious turns up, the minimal-system method strips the bike back to the battery, controller, display and throttle, then adds the other parts back one at a time.
If it won't turn on at all
A completely dark bike, with no display, no lights and no beep, points first at the power chain, and that is walked in a different order:
- Is the pack fully seated in its cradle, and is its own switch or key on? Do its charge LEDs light when you press the button?
- Charge it fully and retry, because a flat pack can look like a dead bike. If the charger shows no sign of charging, stop there and have the pack checked.
- Unplug and inspect the main battery-to-controller plug, then refit it firmly. Look for an inline fuse near the cradle, and for green corrosion or scorch marks on the cradle terminals.
- Then measure: voltage at the pack but none at the controller input puts the break in the plug, fuse or cable between them.
The full sequence is in the power-chain checklist. If the lights work but the screen stays black, see display won't light up. Brand-specific checks: Rad Power Bikes and Super73. Do not open the battery pack; if the measurements point inside it, take it to a service point equipped for lithium packs.
If it cuts out while you ride
When the power drops tells you more than the drop itself.
| When it cuts | Usual cause | Read |
|---|---|---|
| Under hard acceleration or on a climb, back after a short rest | Battery voltage sagging under load until it reaches the low-voltage cut-off | Battery sag or controller? |
| On long climbs, after minutes of steady load | A protection rated for continuous current or heat, not the short peak | Shuts off on hills |
| After a long ride, with the controller hot to the touch | Controller thermal or over-current protection | Battery sag or controller? |
| Over bumps, or when the bars turn | A loose or corroded connector, or a chafed harness | Main wiring harness |
| Jerking or stuttering rather than a clean cut | Usually the Hall signals, the motor plug or the wire order; a battery that sags under load, or the controller, can also cause it | Hall sensor test |
An intermittent cut-out at speed is a crash risk. Stop riding the bike in traffic until you have found the cause.
Before you buy a part
Buy the part a test has pointed at, not the part that seems most likely. The controller comes last because the checks above can rule it in or out before you spend anything. When you are ready, four photos (the display face and model marking, the display connector, the controller label and the motor cable) answer most fit questions; see the four photos we need. Then compare sensors and throttles, wiring or controllers by connector and rating. For the system-by-system view, see e-bike repair DIY.
Sources
The fault-finding order follows the RideRow guides linked above. The supply and signal checks rest on these published service documents, which we cite rather than copy; your bike's own manual takes priority where it differs:
- Grin Technologies, Throttle Testing (PDF): measure the throttle's supply first (roughly 4 to 5 V), then watch the signal rise as the throttle opens.
- Grin Technologies, Hall Sensor Testing (PDF): the Hall supply reads roughly 4 to 5 V, and each signal should switch between about 0 and 5 V as the wheel is turned slowly backwards, so that the rotor really turns (a geared motor freewheels when turned forwards); a signal that never switches points at its wiring or its sensor.
- Pedego, Dealer Service Guide (PDF, error code chart, p. 23): a shorted 5 V circuit is found by unplugging the throttle, the pedal-assist sensor and the motor one at a time.
What we added: the order of the checks, which result points to which part, and when a part is really at fault rather than its plug, wiring or supply.
RideRow is an independent parts retailer and is not affiliated with, endorsed by, or sponsored by any brand named on this page. Brand and model names are trademarks of their respective owners and are used here only to identify the bikes each guide covers. This page is general information for owners who do their own work; RideRow sells parts and publishes how-to guides and does not repair bikes. If you are not confident working on electrical parts, use a qualified e-bike technician.
Last updated: November 2026