Home › Diagnosis › Display works but no assist and no error code: display, controller, motor, battery comms or settings?
Display on, no error, no assist: elimination
DisplayAny e-bike
The hardest fault to read: the bike powers up, shows battery and speed, throws no code, and does nothing when you pedal. This flow works through settings, sensors, battery communication (CAN/UART), firmware and finally the controller and motor, so you end with one named part.
Warning: Rear wheel in the air for all motor tests. Do not open a battery pack.
What you need
- Multimeter
- Display manual or parameter list
- Access to the brand app (Bosch eBike Flow, Shimano E-Tube, Bafang Go/BESST) or the dealer tool for CAN systems
- For UART hub systems: optionally a spare display or controller of the same protocol
LED patterns and what they mean
| Controller and motor fine; PAS/torque sensor or speed sensor | |
| Start condition (brake/throttle), controller drive stage, or a lock/immobiliser | |
| Battery BMS communication lost (CAN/UART) or BMS in protection | |
| Anti-theft lock active (Bosch eBike Lock, Bafang/Shimano app lock, or display PIN) | |
| Interrupted or mismatched firmware between display and controller |
Step by step
1. Assist level, lock and mode
Check the assist level is above 0/OFF. Look for a lock or key icon (Bosch eBike Lock requires the paired phone nearby; some displays have a PIN; some bikes have a GPS immobiliser app). Check the display is not in a 'service' or 'demo' mode.
If OK: Assist level set, no lock. Continue.
If not: Unlock via the app or PIN, raise the assist level. Free fix.
Check the assist level is above 0/OFF. Look for a lock or key icon (Bosch eBike Lock requires the paired phone nearby; some displays have a PIN; some bikes have a GPS immobiliser app). Check the display is not in a 'service' or 'demo' mode.
If OK: Assist level set, no lock. Continue.
If not: Unlock via the app or PIN, raise the assist level. Free fix.
2. Walk assist button
Hold the walk-assist button (usually '-' held, or a dedicated button) with the wheel in the air.
If OK: Motor turns in walk mode: battery, controller drive stage and motor are proven. The fault is the pedal-side input (PAS, torque or speed sensor) or a setting. Go to the pas-cadence-sensor, torque-sensor or speed-sensor flow.
If not: Walk mode does nothing: continue, the problem is upstream of the pedal sensors.
Hold the walk-assist button (usually '-' held, or a dedicated button) with the wheel in the air.
If OK: Motor turns in walk mode: battery, controller drive stage and motor are proven. The fault is the pedal-side input (PAS, torque or speed sensor) or a setting. Go to the pas-cadence-sensor, torque-sensor or speed-sensor flow.
If not: Walk mode does nothing: continue, the problem is upstream of the pedal sensors.
3. Brake and throttle start conditions
Unplug the brake sensors and the throttle (if fitted) one at a time and retry walk mode / throttle / pedal.
If OK: No change. Continue.
If not: Motor runs once a sensor is unplugged: that sensor is stuck. See the brake-cutoff or throttle flow.
Unplug the brake sensors and the throttle (if fitted) one at a time and retry walk mode / throttle / pedal.
If OK: No change. Continue.
If not: Motor runs once a sensor is unplugged: that sensor is stuck. See the brake-cutoff or throttle flow.
4. Battery communication (CAN/UART smart batteries)
On systems where the battery talks to the controller (Bosch, Shimano, Yamaha, Bafang M-series, many 2020+ hub bikes), watch the battery bars: blinking, empty, or a '?' means the BMS is not communicating. Remove the battery, clean the contacts including the small data pins, refit. Try a second battery if you have one.
If OK: Battery level shows correctly and stays stable under walk mode. Continue.
If not: Bars blinking or a second battery fixes it: the battery's BMS communication or its data pins are the fault. Battery repair or replacement; the motor is fine.
On systems where the battery talks to the controller (Bosch, Shimano, Yamaha, Bafang M-series, many 2020+ hub bikes), watch the battery bars: blinking, empty, or a '?' means the BMS is not communicating. Remove the battery, clean the contacts including the small data pins, refit. Try a second battery if you have one.
If OK: Battery level shows correctly and stays stable under walk mode. Continue.
If not: Bars blinking or a second battery fixes it: the battery's BMS communication or its data pins are the fault. Battery repair or replacement; the motor is fine.
5. Battery under load
Watch the display voltage or bars the moment you ask for assist. A pack that sags hard or a BMS that trips will make the display stay on (it needs almost no current) while the motor never gets power.
If OK: Voltage stable when load is requested. Continue.
If not: Voltage drops or the display resets: battery/BMS fault. Fix that first.
Watch the display voltage or bars the moment you ask for assist. A pack that sags hard or a BMS that trips will make the display stay on (it needs almost no current) while the motor never gets power.
If OK: Voltage stable when load is requested. Continue.
If not: Voltage drops or the display resets: battery/BMS fault. Fix that first.
6. Firmware and display/controller pairing
CAN systems: connect the app or dealer tool, check for a pending or interrupted firmware update and that all components are recognised. UART hub systems: check the display's protocol setting matches the controller (Bafang UART vs CAN, KT vs Lishui); a display that shows battery voltage but cannot send commands is the classic mismatch after someone fitted a new display.
If OK: Firmware complete, all components listed, protocol matches. Continue.
If not: Complete the update or fit the correct display. A mismatched display can power up (it only needs battery voltage) yet never command the controller.
CAN systems: connect the app or dealer tool, check for a pending or interrupted firmware update and that all components are recognised. UART hub systems: check the display's protocol setting matches the controller (Bafang UART vs CAN, KT vs Lishui); a display that shows battery voltage but cannot send commands is the classic mismatch after someone fitted a new display.
If OK: Firmware complete, all components listed, protocol matches. Continue.
If not: Complete the update or fit the correct display. A mismatched display can power up (it only needs battery voltage) yet never command the controller.
7. Controller output
Hub systems: measure 5V on the hall and throttle plugs. Try a known-good display of the same protocol, then a known-good controller. Listen for a faint click or hum from the controller when assist is requested. CAN mid-drives: the dealer tool's motor self-test.
If OK: A swapped controller (or the dealer self-test) makes the motor run: the original controller's drive stage or its communication side is dead. Replace it.
If not: Controller passes (or a new controller changes nothing): continue to the motor.
Hub systems: measure 5V on the hall and throttle plugs. Try a known-good display of the same protocol, then a known-good controller. Listen for a faint click or hum from the controller when assist is requested. CAN mid-drives: the dealer tool's motor self-test.
If OK: A swapped controller (or the dealer self-test) makes the motor run: the original controller's drive stage or its communication side is dead. Replace it.
If not: Controller passes (or a new controller changes nothing): continue to the motor.
8. Motor: halls and phases
Hub motors: hall test (three signals toggle) and phase resistance (three equal low readings, none to case). Mid-drives: noise test and dealer readout.
If OK: Motor tests good. By elimination, and if a swap controller did not fix it, re-check the harness between controller and motor for a broken wire; that is the last remaining link.
If not: Hall or phase fault: motor repair or replacement. Note that many controllers show no code for an open phase until the motor is asked to turn.
Hub motors: hall test (three signals toggle) and phase resistance (three equal low readings, none to case). Mid-drives: noise test and dealer readout.
If OK: Motor tests good. By elimination, and if a swap controller did not fix it, re-check the harness between controller and motor for a broken wire; that is the last remaining link.
If not: Hall or phase fault: motor repair or replacement. Note that many controllers show no code for an open phase until the motor is asked to turn.
What you now know for sure
- Setting or lock: Assist 0, lock/PIN active, demo mode. → Change setting, unlock. Free.
- Pedal-side sensor: Walk mode works, pedalling does not. → PAS, torque or speed sensor flow.
- Brake/throttle stuck: Runs once a sensor is unplugged. → Replace the sensor.
- Battery communication or BMS: Bars blinking, battery not recognised, or collapse under load. → Clean data pins; battery repair/replacement.
- Firmware / display mismatch: Display powers but cannot command the controller. → Complete update; fit matching display.
- Controller or motor: Everything upstream proven; swap or self-test isolates which. → Replace the failed unit; see controller-test and hub-motor flows.
Manuals and video
Videos found on YouTube and checked automatically; they are other people's work, not ours.
- How to Fix Ebike Error Code 10/11: Troubleshooting Controller & SW900 LCD Voilamart Ebike
- How to Bypass an E-Bike Display ElectronicLab
- how to use electric bike without display Saam E-bike
Frequently asked
How can the display show everything normally while the motor does nothing?
The display only needs a few milliamps from the controller's logic side and reads battery voltage. The drive stage that powers the motor, the sensors that tell it to start, and the battery's ability to deliver current are all separate, and any of them can fail silently.
No error code at all: is that good or bad news?
Mixed. It rules out the faults the controller can detect on its own (hall, phase, speed sensor, brake). It leaves settings, battery communication, a stuck start condition, or a drive stage that dies only under load. Walk mode is your fastest divider.
I fitted a new display and now there is no assist.
Almost certainly a protocol mismatch (UART vs CAN, or KT vs Bafang vs Lishui). The display lights because it gets battery voltage, but it speaks the wrong language to the controller. Fit a display made for your controller.
Still stuck? Take a photo of the display and show it to a local e-bike workshop. Bring the bike's system name (e.g. Bosch Performance Line CX) and the exact code; that saves diagnostic time and money.