Motor cuts out or power comes and goes

Power that comes and goes is often harder to diagnose than power that's gone, because the fault hides when the bike is still. Notice when it happens: over bumps, on hills, when it's wet, or at random.

Over bumps

That points at a connection that moves. Himiway says vibration and rough ground can make loose connectors or corroded pins lose contact (Himiway). With the bike off and the battery out:

• Check the battery is fully seated and locked (Himiway).
• Check the plugs at the handlebar and along the frame. Pull each straight apart, don't twist, and push it back with the arrows lined up (Lectric quick plug check).
• On a rear hub motor, check the motor cable plug near the axle. Lectric notes this plug doesn't click, so press it firmly home (Lectric quick plug check, Lectric E007).

On hills or when you push hard

• A low, cold or worn battery may not hold voltage under load. Test on flat ground with a full charge. If it only cuts out under heavy load, the battery may be the cause (Himiway). See battery dies fast.
• Long climbs, heavy cargo and hot weather can trip thermal protection. Let the bike cool, Himiway suggests 15 to 30 minutes, and see if it comes back (Himiway). Bafang's code list includes motor and controller overheating (Bafang C271 manual).

When you touch the brakes

Many e-bikes cut the motor when a brake lever is pulled. A lever that doesn't spring fully back can keep that cut-off active, so check both levers return (Velotric troubleshooting). An overly sensitive brake sensor can also tell the controller you're braking when you aren't (Himiway). Don't remove or bypass brake sensors. Have a shop check them.

At speed, or random

A dirty or misaligned speed sensor magnet can make the controller lose the speed signal and cut power (Himiway, Himiway speed sensor). Clean the sensor and magnet and check the magnet passes the sensor's mark. See no pedal assist.

Get it checked if

• Assist keeps cutting out at a normal charge level (Velotric troubleshooting).
• An error code comes with the cut-outs. See error codes.
• It cut out in traffic. Himiway warns sudden cut-offs at intersections or on climbs can upset your balance (Himiway speed sensor).

Sources

• Why does my ebike motor keep cutting out, Himiway
• Quick connect plug check, Lectric eBikes
• Error code E007, Lectric eBikes
• C271 display user manual, Bafang
• Electric bike troubleshooting guide, Velotric
• Ebike not reading speed, Himiway

Stuck after these checks? Find a shop near you.