Display, Controller and Remote: How the Parts Fit Together

A code says "display" or "controller" and you can't tell which lump of plastic that is. Here's how the parts split up, so a maker's wording starts to make sense.

The three names you'll meet

Makers use different words, so the same part can have two names.

• Display. The screen on the handlebar. It shows your speed, assist setting and battery charge, and it shows codes.
• Button pad. The set of buttons you press to change the assist or scroll the screen. Some bikes build the buttons into the display. Others put them in a separate unit by the grip, which many people call the remote.
• Controller. A unit that manages the motor. One maker's list says it "relies on accurate data transmission to regulate functions such as power assistance levels and motor control"¹. Which exact box does this varies by make, so check your manual.

The trade term HMI shows up in maker lists. It stands for human-machine interface. It covers the parts you use to talk to the bike, meaning the screen and the buttons.

Why the split matters when something fails

A maker's code list shows the split plainly. One list has an entry "84 | Controller - Controller communication error" and another reading "100 | HMI - Display panel malfunction"². The first points at the controller. The second points at the screen. They're different parts, with different fixes.

For the controller entry, the maker's description says "System communication with the controller is interrupted due to a potential connection issue between components"¹. In plain words, if the link breaks, the assist can misbehave.

Notice the wording: a connection issue. A code that names a part doesn't prove that part has failed.

One code, several suspects

For the display panel entry, the maker's list of possible causes reads "Defective HMI Defective Controller Damaged extension cable"¹. That's three suspects for one code. The screen, the controller and the cable between them can each be the cause. That's why makers tell you to follow their steps in order rather than guess.

A rough order, adapted to the way these lists read:

1. Note the exact code and write it down.
2. Switch the system off and on again, following your manual.
3. Look at the battery seat and any visible plug or cable. Don't pull apart sealed parts.
4. If the code returns, take it to the maker or a dealer with the code written down.

Throttle and pedal sensor

Some bikes also have a throttle. Wikipedia describes "power-on-demand", where "the motor is activated by a throttle"³. A throttle is one more input that reaches the controller. If your bike has one, your manual will show where it plugs in.

What the screen can't settle

The display is where you read the news, and it isn't always where the trouble starts. Don't replace a screen on a guess. Look the code up in your manual first (how to do that). For the symbols on the screen itself, see the icons page.