Rad Power Bikes display error 25

What Error 25 Means

Error 25 means the controller is detecting an abnormal brake-cutoff signal.

E-bikes commonly have electrical switches in the brake levers. When you squeeze a brake, that switch tells the controller to immediately stop sending power to the motor.

In plain English, the bike thinks a brake is being applied when it should not be, or it is not receiving the brake signal it expects. To stay safe, the controller may disable motor assistance.

Brake lever held during startup

Brake lever that does not return completely

Stuck or damaged brake cutoff switch

• Loose brake sensor connector

• Water or dirt inside a connector

• Bent or damaged connector pins

Damaged brake sensor wiring

Fault elsewhere in a shared wiring circuit on some bikes

Before You Touch Anything

Turn the bike off and remove the battery before disconnecting electrical connectors. Check both brake levers first. Do not ride the bike if:

A brake lever sticks or does not return normally

The brakes themselves are not working correctly

• The motor continues powering the bike while a brake is applied

Brake wiring or connectors are visibly damaged

1. Release Both Brake Levers

Error 25 can sometimes appear because a brake lever was being squeezed when the bike was turned on. Make sure both levers are completely released.

Squeeze and release each lever several times. They should return freely to their normal position. Restart the bike without touching either brake.

2. Inspect the Brake Levers

With the bike turned off, look closely at both brake levers.

Lever feels sticky

Lever does not return all the way

Damage from a fall or impact

• Bent lever

Grip, accessory, cable, or other object preventing full movement

If a lever is damaged or does not return properly, have the brake repaired before continuing.

3. Check the Brake Sensor Connectors

Turn the bike off and remove the battery. Follow the electrical wire from each brake lever toward the wiring harness. Start with one brake connector.

Pull the two sides straight apart. Do not twist the connector and do not pull on the wires.

4. Inspect the Connector

• Water or moisture

• Dirt or debris

• Bent pins

• Corrosion

Pushed-back pins

Damaged wiring

Cracked connector housing

5. Reconnect the Brake Sensor

If everything looks clean and undamaged, line up the arrows, pins, or alignment marks and push the connector straight together without twisting. Make sure it is fully seated. Repeat the inspection for the other brake lever if necessary.

6. Restart and Check the Bike

Reinstall the battery. Make sure both brake levers are completely released and turn the bike on.

If Error 25 is gone, check the bike carefully before riding. When operating normally, applying either brake should immediately stop motor assistance.

If motor power continues while a brake is applied, stop riding and have the brake cutoff system inspected.

Error 25 Still Showing?

Failed brake cutoff sensor

Damaged brake sensor wiring

Wiring harness problem

Controller input fault

Another component sharing the same circuit on certain bike models

A Note About Taillights on Some Rad Bikes

Rad Power Bikes includes taillight connections in its Error 25 troubleshooting process on certain models. That does not mean every Error 25 is a taillight problem. On some Rad electrical systems, the brake sensors, brake-light circuit, and related wiring interact closely enough that a fault elsewhere in that circuit can contribute to the error.

For a generic e-bike guide, start with the brake levers, brake switches, and their connectors. Brand-specific shared wiring should be diagnosed according to the manufacturer's documentation.

Quick Answer

Error 25 = brake cutoff switch fault.

The controller is receiving an abnormal brake signal and may disable motor power because it thinks a brake is being applied.

1. Completely release both brake levers.

2. Restart the bike without touching the brakes.

3. Make sure both brake levers move and return normally.

4. Check both brake sensor connectors.

5. Look for water, dirt, bent pins, or damaged wiring.

6. Reconnect the brake connectors firmly without twisting.

7. If Error 25 returns, have the brake sensors, wiring, and controller tested.

Do not ride the bike if a brake lever sticks, the brakes are not functioning correctly, or motor power continues while a brake is applied.

Source & Compatibility

KEY-DISP KD21C: Defines Code 25 as "Brake Abnormality." KD21C manual

Rad Power Bikes: Lists Error 25 as "Brake switch fault or the brake applied while turning on." Rad owner-manual reference

Error numbers are not universal across all e-bikes. Another display, controller, or motor system may use the same number for a different problem. Confirm the bike's electrical platform before applying this troubleshooting procedure.

How the Five Codes Differ

Code

System Area

What the Controller Is Seeing

21

Current protection

The controller measured current outside its expected range.

22

Rider input

The throttle signal is abnormal.

23

Motor power circuit

The controller is not seeing the expected response from the motor phase circuit.

24

Motor feedback

The controller is not receiving reliable motor-position information.

25

Brake safety input

The controller is receiving an abnormal brake-cutoff signal.

General Safety Rules for Electrical Error Codes

Turn the bike off and remove the battery before unplugging electrical connectors.

Pull waterproof connectors straight apart and push them straight together. Do not twist them.

Do not force bent, misaligned, burned, or melted connectors back together.

Stop if you find unusual heat, burning odor, melted plastic, damaged wiring, or unpredictable motor behavior.

Do not keep resetting a recurring ride-stopping fault as a substitute for diagnosis.

After any repair or reconnection, test the bike cautiously in a controlled area before normal riding.

Source Notes

The code definitions in this guide are based on the KEY-DISP KD21C error-code table and Rad Power Bikes owner-manual/support terminology. Rad-specific troubleshooting steps may vary by model and model year.

KEY-DISP KD21C user manual | Rad Power Bikes owner-manual error-code reference

Editorial note: This is a plain-English troubleshooting reference, not a replacement for the manufacturer's service manual or hands-on diagnosis by a qualified e-bike technician.