Pedal assist dead but throttle works (or vice versa)? Here are the 7 most common causes and how to fix each one — from a working mobile eBike mechanic.
Pedal assist (PAS) failing is one of the top three calls I get every week. The good news: it's almost always one of seven things, and most are quick fixes.
The PAS sensor lives near the bottom bracket. Its connector vibrates loose or corrodes — especially on bikes ridden near the coast. Unplug, inspect for corrosion, reseat firmly. Fix rate: ~40% of PAS issues.
Cadence-based systems use a disc of magnets that spins past a sensor. If the disc has slid along the crank or warped, the sensor can't read it. Re-center the disc 1–3mm from the sensor face. If a magnet is missing, replace the disc ($15–$30).
Sounds dumb, but I've driven out for this one. Check the display — some bikes default to PAS 0 after a hard reboot.
Most eBikes cut motor power when you squeeze the brake. If a brake lever sensor is stuck "on," PAS will never engage. Squeeze and release each lever and watch for the motor cutoff indicator on the display.
Some systems use a speed sensor on the rear wheel to enable PAS above 0 mph. If the speed sensor magnet is missing or misaligned, PAS won't kick in. Look at the rear dropout for a small sensor and a matching magnet on a spoke.
On Aventon and newer Bafang systems, a firmware hiccup can disable PAS while throttle still works. A hard reset (battery off + display off for 5 minutes) clears it about half the time.
If everything above checks out and PAS still won't engage, the controller's PAS input has likely failed. See our controller troubleshooting guide. Replacement is typically required.
1. Check display PAS level (10 seconds) 2. Squeeze both brake levers and release (15 seconds) 3. Inspect PAS sensor connector (2 minutes) 4. Inspect magnet disc alignment (3 minutes) 5. Hard reboot (5 minutes) 6. Inspect speed sensor (2 minutes) 7. Call us — likely controller (5 seconds)
If the bike is acting weird, don't crank up the throttle to "test" it. A failing controller can take the motor or battery with it. We do same-day PAS diagnostics across North County — bring it back to life without a shop trip.
Coastline Fix is North County San Diego's mobile eBike mechanic. We come to you — same-day or next-day.