Home › Diagnosis › Is my hub motor dead? Elimination test: motor vs controller vs display vs sensor vs battery
Is my hub motor dead? The full elimination flowchart
Motor & controllerHub motors (Bafang, generic, Rad, Aventon, ADO, Fiido, Engwe, Himiway)
A hub-motor e-bike that gives no assist has five suspects: battery, display, brake/throttle/PAS sensors, controller and the motor itself. This flow eliminates them one by one, cheapest test first, until only one is left.
Warning: Work with the battery switched off and unplugged when you open connectors. Never short phase wires with the battery connected. Lift the rear wheel off the ground (stand or hang the bike) before any test that could spin it, and keep fingers, tools and cables away from the spokes.
What you need
- Digital multimeter (DC volts, ohms, continuity beep)
- A stand or hook so the driven wheel can spin freely
- Small flat screwdriver or pins to back-probe connectors
- Zip ties or tape to hold connectors during tests
- Optional: a known-good controller of the same voltage and connector type
- 20-40 minutes, dry workspace
LED patterns and what they mean
| Power stops between battery and display: main fuse, key switch, display cable, controller 5V rail | |
| Controller not getting a valid start condition (brake, throttle, PAS) or motor drive stage dead | |
| Controller cannot read a hall sensor: hall wiring, hall sensor, or controller input | |
| Open phase wire, blown phase connector, or shorted winding | |
| Classic single-hall-dead or one-phase-open behaviour | |
| Shorted winding, shorted controller MOSFET, or mechanical jam |
Step by step
1. Battery: is it really delivering voltage under load?
Charge fully. Measure the battery output pins: a 36V pack should read 40-42V, a 48V pack 52-54.6V, a 52V pack 56-58.8V. Then hold the throttle (or pedal) while watching the display's voltage or bars. If the pack reads fine at rest but the display reboots or drops 5-10V the moment the motor is asked for power, the BMS or a cell group is cutting out.
If OK: Voltage at rest is in range and does not collapse under load. Battery is cleared. Continue.
If not: Low voltage, no voltage, or collapse under load: this is a battery/BMS problem, not a motor problem. Stop here and diagnose the pack (charger, BMS reset by charging, cell balance, dead cell group). A motor cannot be tested on a bad battery.
Charge fully. Measure the battery output pins: a 36V pack should read 40-42V, a 48V pack 52-54.6V, a 52V pack 56-58.8V. Then hold the throttle (or pedal) while watching the display's voltage or bars. If the pack reads fine at rest but the display reboots or drops 5-10V the moment the motor is asked for power, the BMS or a cell group is cutting out.
If OK: Voltage at rest is in range and does not collapse under load. Battery is cleared. Continue.
If not: Low voltage, no voltage, or collapse under load: this is a battery/BMS problem, not a motor problem. Stop here and diagnose the pack (charger, BMS reset by charging, cell balance, dead cell group). A motor cannot be tested on a bad battery.
2. Does the display turn on and stay on?
Press and hold the power button 2-3 seconds. Watch for backlight, digits, wheel icon. Wiggle the display cable at the bar and at the controller junction while it is on.
If OK: Display is on and stable. It is receiving 5V/36V/48V from the controller, so the controller's logic side is at least partly alive. Continue.
If not: No display at all: follow the display-blank flow first. Display flickers when you move the cable: damaged display cable or corroded connector, fix before anything else. A dead display does not mean a dead motor.
Press and hold the power button 2-3 seconds. Watch for backlight, digits, wheel icon. Wiggle the display cable at the bar and at the controller junction while it is on.
If OK: Display is on and stable. It is receiving 5V/36V/48V from the controller, so the controller's logic side is at least partly alive. Continue.
If not: No display at all: follow the display-blank flow first. Display flickers when you move the cable: damaged display cable or corroded connector, fix before anything else. A dead display does not mean a dead motor.
3. Read the error code, if any
Note the exact code on the display. Bafang UART displays: 08 = hall sensor, 09 = phase, 21 = speed sensor, 03 = brake, 04/05 = throttle, 30 = communication. KT LCD3/LCD8: 03H = motor hall, 01H = throttle, 06H = undervoltage. Look the code up on this site under your display brand.
If OK: No error code: the controller sees nothing wrong on power-up, which points to a start-condition problem (brake, throttle, PAS) or a motor drive stage that only fails under load. Continue with step 4.
If not: There is a code. Hall/phase codes (08/09/03H) take you straight to steps 7-9. Brake/throttle codes take you to steps 4-5. Speed sensor codes: see the speed-sensor flow.
Note the exact code on the display. Bafang UART displays: 08 = hall sensor, 09 = phase, 21 = speed sensor, 03 = brake, 04/05 = throttle, 30 = communication. KT LCD3/LCD8: 03H = motor hall, 01H = throttle, 06H = undervoltage. Look the code up on this site under your display brand.
If OK: No error code: the controller sees nothing wrong on power-up, which points to a start-condition problem (brake, throttle, PAS) or a motor drive stage that only fails under load. Continue with step 4.
If not: There is a code. Hall/phase codes (08/09/03H) take you straight to steps 7-9. Brake/throttle codes take you to steps 4-5. Speed sensor codes: see the speed-sensor flow.
4. Brake cut-off levers: is one sensor stuck 'on'?
With the display on, look for a brake icon or an 'E' and a hand symbol. Then unplug both brake sensor connectors (2-pin or 3-pin, usually near the stem) and try the throttle or pedal.
If OK: No brake symbol and the motor still does nothing with brakes unplugged. Brake sensors are cleared. Plug them back in. Continue.
If not: The motor runs the moment a brake sensor is unplugged: that sensor (or its lever magnet, or a pinched wire) is stuck. Replace the sensor or lever. See the brake-cutoff flow. Do not ride with sensors disconnected long-term.
With the display on, look for a brake icon or an 'E' and a hand symbol. Then unplug both brake sensor connectors (2-pin or 3-pin, usually near the stem) and try the throttle or pedal.
If OK: No brake symbol and the motor still does nothing with brakes unplugged. Brake sensors are cleared. Plug them back in. Continue.
If not: The motor runs the moment a brake sensor is unplugged: that sensor (or its lever magnet, or a pinched wire) is stuck. Replace the sensor or lever. See the brake-cutoff flow. Do not ride with sensors disconnected long-term.
5. Throttle test (if the bike has one)
Wheel in the air, display on. Press the throttle. If nothing: back-probe the throttle connector. Red-black should read ~5V. Signal-black should read 0.8-1.0V at rest and rise smoothly to 3.6-4.2V at full twist.
If OK: Throttle spins the wheel: the controller, hall sensors, phase wires and motor windings are all working. Your no-assist problem is on the pedal side (PAS sensor or torque sensor). Skip to step 6 and stop after it.
If not: Throttle signal is correct but the wheel does not move: the problem is downstream (controller drive stage, halls, phases, motor). Throttle signal wrong or missing: throttle is faulty, but that alone does not explain a dead pedal assist. Continue.
Wheel in the air, display on. Press the throttle. If nothing: back-probe the throttle connector. Red-black should read ~5V. Signal-black should read 0.8-1.0V at rest and rise smoothly to 3.6-4.2V at full twist.
If OK: Throttle spins the wheel: the controller, hall sensors, phase wires and motor windings are all working. Your no-assist problem is on the pedal side (PAS sensor or torque sensor). Skip to step 6 and stop after it.
If not: Throttle signal is correct but the wheel does not move: the problem is downstream (controller drive stage, halls, phases, motor). Throttle signal wrong or missing: throttle is faulty, but that alone does not explain a dead pedal assist. Continue.
6. PAS (cadence) sensor test
Wheel in the air, display on, assist level 1 or higher. Spin the cranks forward by hand slowly. Watch the PAS connector with a meter: red-black ~5V, signal-black should toggle between ~0V and ~5V (or ~1V and ~4V) as the magnet disc passes the sensor, typically 6-12 pulses per crank revolution. Check the magnet ring is not cracked, has not slipped away from the sensor (gap should be 1-3 mm) and is facing the correct direction.
If OK: Signal pulses and the motor runs when you pedal: PAS is fine. If the throttle also worked in step 5, the bike is now working and the original fault was intermittent (loose connector). Go to step 10.
If not: No pulses: PAS sensor, magnet ring or wiring. Cheap part, replace it. Pulses present but no assist while the throttle also fails: the fault is downstream. Continue to the hall test.
Wheel in the air, display on, assist level 1 or higher. Spin the cranks forward by hand slowly. Watch the PAS connector with a meter: red-black ~5V, signal-black should toggle between ~0V and ~5V (or ~1V and ~4V) as the magnet disc passes the sensor, typically 6-12 pulses per crank revolution. Check the magnet ring is not cracked, has not slipped away from the sensor (gap should be 1-3 mm) and is facing the correct direction.
If OK: Signal pulses and the motor runs when you pedal: PAS is fine. If the throttle also worked in step 5, the bike is now working and the original fault was intermittent (loose connector). Go to step 10.
If not: No pulses: PAS sensor, magnet ring or wiring. Cheap part, replace it. Pulses present but no assist while the throttle also fails: the fault is downstream. Continue to the hall test.
7. Hall sensor test: the three signal wires
Unplug the motor's 9-pin (or separate 5/6-pin hall) connector from the controller. On the motor side: with the controller side plugged in and powered, or with an external 5V source, feed 5V (red) and ground (black) to the hall side. Put the meter between black and each of the three hall signal wires (yellow, green, blue) in turn. Slowly rotate the wheel by hand. Each signal must switch cleanly between low (0-0.5V) and high (4-5V) several times per revolution. Alternative without power: on the controller-side connector measure 5V on red-black. If 5V is missing the controller's hall supply is dead.
If OK: All three halls toggle: hall sensors and their wiring are good. Continue to phase test.
If not: One hall stuck high or low, or never changes: dead hall sensor or broken hall wire. This causes stuttering, kick-back or a hall error code. Repair = replace the hall board/sensors inside the motor (cheap parts, fiddly labour) or the axle cable. If 5V is missing from the controller side, the controller is the fault, not the motor.
Unplug the motor's 9-pin (or separate 5/6-pin hall) connector from the controller. On the motor side: with the controller side plugged in and powered, or with an external 5V source, feed 5V (red) and ground (black) to the hall side. Put the meter between black and each of the three hall signal wires (yellow, green, blue) in turn. Slowly rotate the wheel by hand. Each signal must switch cleanly between low (0-0.5V) and high (4-5V) several times per revolution. Alternative without power: on the controller-side connector measure 5V on red-black. If 5V is missing the controller's hall supply is dead.
If OK: All three halls toggle: hall sensors and their wiring are good. Continue to phase test.
If not: One hall stuck high or low, or never changes: dead hall sensor or broken hall wire. This causes stuttering, kick-back or a hall error code. Repair = replace the hall board/sensors inside the motor (cheap parts, fiddly labour) or the axle cable. If 5V is missing from the controller side, the controller is the fault, not the motor.
8. Phase-to-phase resistance and continuity
Battery unplugged, motor phase connector unplugged from the controller. Measure resistance between each pair of the three thick phase wires (yellow-green, green-blue, blue-yellow). All three readings must be nearly identical and very low (typically 0.1-2 ohm, most cheap meters just show a few tenths of an ohm). Then measure from each phase wire to the axle/motor casing.
If OK: Three equal low readings, no continuity to the casing: windings are intact and not shorted to ground. Continue.
If not: One pair reads open (OL) or clearly different: open winding or broken phase wire at the axle (very common where the cable exits the axle). Any continuity to the casing: winding shorted to ground, motor is scrap or needs rewinding. A melted or discoloured phase connector at the controller means the connector, not the motor, failed.
Battery unplugged, motor phase connector unplugged from the controller. Measure resistance between each pair of the three thick phase wires (yellow-green, green-blue, blue-yellow). All three readings must be nearly identical and very low (typically 0.1-2 ohm, most cheap meters just show a few tenths of an ohm). Then measure from each phase wire to the axle/motor casing.
If OK: Three equal low readings, no continuity to the casing: windings are intact and not shorted to ground. Continue.
If not: One pair reads open (OL) or clearly different: open winding or broken phase wire at the axle (very common where the cable exits the axle). Any continuity to the casing: winding shorted to ground, motor is scrap or needs rewinding. A melted or discoloured phase connector at the controller means the connector, not the motor, failed.
9. Spin the wheel by hand: cogging test for a shorted phase
Phase connector still unplugged from the controller. Spin the wheel and feel. A geared hub should freewheel silently. A direct-drive hub should turn with a light, even magnetic drag. Now briefly twist two phase wires together (battery still unplugged!) and spin again: a direct-drive motor should become noticeably harder to turn (it is generating into a short).
If OK: Free or lightly even spin unplugged, much stiffer with two phases shorted: windings and magnets are healthy. The motor is cleared. Continue to step 10.
If not: Heavy, lumpy, notchy resistance with the phases unplugged: internal short in the windings or a broken magnet, motor is dead. If the wheel is lumpy only while plugged into the controller, a controller MOSFET is shorted: replace the controller, not the motor.
Phase connector still unplugged from the controller. Spin the wheel and feel. A geared hub should freewheel silently. A direct-drive hub should turn with a light, even magnetic drag. Now briefly twist two phase wires together (battery still unplugged!) and spin again: a direct-drive motor should become noticeably harder to turn (it is generating into a short).
If OK: Free or lightly even spin unplugged, much stiffer with two phases shorted: windings and magnets are healthy. The motor is cleared. Continue to step 10.
If not: Heavy, lumpy, notchy resistance with the phases unplugged: internal short in the windings or a broken magnet, motor is dead. If the wheel is lumpy only while plugged into the controller, a controller MOSFET is shorted: replace the controller, not the motor.
10. Controller: signs of failure and the swap test
Smell the controller and its connectors: a sweet burnt-electronics smell or brown marks on the case are a MOSFET or capacitor failure. Check the controller LED (if present) lights up. Measure 5V on the hall and throttle connectors. Then, if you have one, plug in a known-good controller of the same voltage, current class and connector layout and repeat the throttle test.
If OK: Everything upstream and inside the motor tests good but the wheel still will not spin: by elimination this is the controller's drive stage (dead MOSFET, blown gate driver). Replace the controller.
If not: Burnt smell, scorch marks, missing 5V or a swap controller makes the motor run: the controller is the fault. Before fitting the new one, check why it died: a shorted hall wire, a motor winding short or water ingress will kill the replacement too. See the controller-test flow for matching a replacement.
Smell the controller and its connectors: a sweet burnt-electronics smell or brown marks on the case are a MOSFET or capacitor failure. Check the controller LED (if present) lights up. Measure 5V on the hall and throttle connectors. Then, if you have one, plug in a known-good controller of the same voltage, current class and connector layout and repeat the throttle test.
If OK: Everything upstream and inside the motor tests good but the wheel still will not spin: by elimination this is the controller's drive stage (dead MOSFET, blown gate driver). Replace the controller.
If not: Burnt smell, scorch marks, missing 5V or a swap controller makes the motor run: the controller is the fault. Before fitting the new one, check why it died: a shorted hall wire, a motor winding short or water ingress will kill the replacement too. See the controller-test flow for matching a replacement.
11. Final ride test and load check
Reassemble, dry all connectors, apply dielectric grease. Ride at assist level 1, then max, on a small hill. Watch for cut-outs, stuttering, or the display rebooting under load.
If OK: Consistent assist under load: repair confirmed.
If not: Works unloaded but fails on a hill: battery sag (step 1), a phase connector that opens under current, or a marginal hall. Repeat steps 1, 7 and 8 while a helper applies load with the brake.
Reassemble, dry all connectors, apply dielectric grease. Ride at assist level 1, then max, on a small hill. Watch for cut-outs, stuttering, or the display rebooting under load.
If OK: Consistent assist under load: repair confirmed.
If not: Works unloaded but fails on a hill: battery sag (step 1), a phase connector that opens under current, or a marginal hall. Repeat steps 1, 7 and 8 while a helper applies load with the brake.
What you now know for sure
- Battery or BMS: Voltage low, absent, or collapses under load. Nothing downstream can be judged until this is fixed. → Charge, test cells, replace BMS or pack. Do not buy a motor or controller.
- Display or display cable: Display blank or flickering; controller may be fine. → Follow the display-blank flow; replace cable or display.
- Brake, throttle or PAS sensor: Motor runs once the faulty sensor is unplugged or replaced. Motor and controller are healthy. → Replace the sensor (10-30 EUR/USD). Cheapest outcome.
- Hall sensor / hall wiring: One or more hall signals do not toggle. Motor stutters or throws error 08 / 03H. → Replace hall sensors (needs motor opened) or the axle cable; or run the controller in sensorless mode if it supports it.
- Controller: Burnt smell, missing 5V, lumpy wheel only when plugged in, or a swap controller fixes it. → Replace with a matched controller. Find the reason it died first.
- Motor windings or magnets: Open phase, phase shorted to casing, or lumpy drag with phases unplugged. → New motor or professional rewind. On cheap hubs a complete motor is usually cheaper than a repair.
Manuals and video
Frequently asked
Can a hub motor be dead while the display works perfectly?
Yes. The display is powered by the controller's logic side, which is separate from the drive stage that powers the motor. A working display only proves the battery and the controller's low-voltage circuits are alive.
What does a burnt smell from the motor or controller mean?
Burnt varnish smell from the motor means overheated windings, usually from climbing long hills at low speed; measure phase resistance and check for shorts to the casing. A sharp electronics smell from the controller means a blown MOSFET or capacitor. Either way, do not keep riding it.
My motor stutters and kicks back rather than being fully dead. Which part is it?
Almost always a hall sensor or one hall wire, occasionally one open phase. Do the hall test in step 7: one of the three signals will not toggle. Sensorless controllers can mask a bad hall at speed but still stutter from standstill.
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.