FIRST SPLIT
Find out whether one input has failed or both
This is the fastest way to narrow the problem. PAS and throttle are separate inputs, but they often share the same controller, brake cutoffs, power supply, and wiring harness.
With the bike safely supported, test PAS and throttle separately. Note whether one still works, both fail, or the motor responds intermittently.
- Only PAS fails: focus on PAS sensor setup, connector, and signal.
- Only throttle fails: focus on throttle connector, wiring, and signal.
- Both fail: check shared causes first, especially brake cutoffs, sensor power, and controller-side wiring.
SHARED CUTOFF
Rule out the brake cutoffs
A stuck or damaged brake sensor can tell the controller to disable motor power. Because that cutoff can affect both PAS and throttle, it is one of the first shared faults to eliminate.
Inspect the brake sensor connectors. If appropriate for your system, temporarily disconnect the brake cutoff sensors and test PAS and throttle again.
- Inputs work again: troubleshoot the brake sensor, lever, connector, or wiring.
- No change: continue to the input connectors and wiring.
INPUT WIRING
Inspect the PAS and throttle connectors
Input faults are often caused by something simpler than a failed sensor. A loose waterproof connector, bent pin, pushed-back terminal, damaged cable, or corrosion can stop the signal from reaching the controller.
Disconnect and inspect the PAS and throttle connectors one at a time. Check alignment marks, pin condition, corrosion, cable damage, and whether each connector is fully seated.
- Loose or damaged connection found: correct it and retest before replacing the sensor.
- Connections look good: continue to the PAS- or throttle-specific checks.
PAS-SIDE CHECK
Check PAS sensor position and magnet movement
A PAS sensor needs to detect the magnet ring or magnetic rotor as the cranks turn. If the sensor is too far away, misaligned, loose, or the magnet ring has shifted, pedal assist may stop even though the rest of the bike works normally.
Inspect the PAS sensor and magnet ring near the crank. Make sure the ring turns with the crank, the magnets are intact, and the sensor sits close enough to the ring without rubbing.
- Misalignment or loose ring found: correct the setup and retest PAS.
- Mechanical setup looks correct: the PAS signal or wiring may need electrical testing.
- Problem started after changing settings or replacing a display/controller: verify the PAS-related settings for your system.
THROTTLE-SIDE CHECK
Check the throttle for a clean, normal return
A damaged throttle can fail mechanically or electrically. Before probing wires, make sure the throttle moves freely and returns normally without sticking.
Inspect the throttle body and cable. Make sure it moves smoothly, returns fully, and has no obvious damage near the handlebar, connector, or cable exit.
- Mechanical damage or sticking found: repair or replace the throttle before deeper testing.
- Throttle feels normal: continue to sensor power and signal checks if the fault remains.
SENSOR POWER
Check whether the controller is powering the inputs
PAS and throttle sensors usually need a low-voltage supply from the controller, often around 5V. If that supply is missing, one or both inputs may stop working even though the display still turns on.
First inspect the connectors for loose pins or damaged wires. If you know the connector pinout and are comfortable using a multimeter, set it to DC volts and measure the sensor supply. Do not probe unknown pins blindly.
- Around 5V present: the controller is supplying sensor power. Continue with signal-specific testing.
- 0V: investigate controller sensor power, wiring, or a shorted accessory before replacing PAS or throttle.
NARROW THE FAULT
Separate sensor faults from controller-side faults
By this point, you should know whether the problem affects one input or both, whether the brake cutoffs are involved, whether the connectors are sound, and whether sensor power is present.
If sensor power is present but one input still does not work, test that input's signal using the correct pinout for your system. If both inputs fail despite good power and wiring, controller-side diagnosis becomes more important.
- One input fails while the other works: stay focused on that sensor, connector, and signal wire.
- Both inputs fail with good wiring and sensor power: investigate shared controller inputs or system-specific settings.
Common questions
Why does the throttle work but PAS does not?
That usually means the motor and main power system are still working. Focus on the PAS sensor, magnet ring, connector, alignment, display settings, and PAS signal.
Why does PAS work but the throttle does not?
Focus on the throttle itself, its connector, wiring, and signal. Some systems also disable or limit throttle operation through settings, so system-specific configuration may need to be checked.
If both PAS and throttle stop working, is the controller bad?
Not necessarily. A shared brake cutoff, missing sensor supply, damaged harness, connector problem, or controller-side fault can all affect both inputs.
Keep the diagnostic checklist on your bench.
Use the EbikeFixIt Quick Diagnostic Guide while you work through a fault.