APT-style colour displays keep their fault list short. Seven numbered codes cover everything the controller reports, and the two manufacturer display manuals behind this table — one for the 750C, one for the 850C — carry the same seven entries. One reference therefore covers both screens, which is unusual in a market where almost every display numbers its faults differently.
The seven codes
01 — Communication error. The display and the controller are not exchanging data. Expect this one after a display swap or after work around the head tube. Check the communication connector before suspecting either component: a single bent pin, or a cable pinched where the bars turn, produces exactly this code.
02 — Controller protection. The manual sends you to the three phase wires. The controller has shut itself down rather than drive a load it cannot read properly, so look at the thick motor leads and their connector rather than at the screen.
03 — Three-phase power error. The phase connection itself. In practice 02 and 03 arrive from the same place, and the same inspection answers both — see the section below.
04 — Battery low. Charge the pack. If the code comes back quickly on a pack that reads healthy at rest, the likely cause is voltage sag under load rather than anything wrong with the display.
05 — Brake error. The brake connection. A lever held down, a sensor stuck on, or water in one of the two brake connectors will each report this. Unplug the brake sensors one at a time; the code clearing tells you which side was reporting.
06 — Throttle error. The throttle connection. Most often the throttle is not returning to rest, or moisture has got into its plug. Unplug it: if the code clears with the throttle disconnected, that is the part to change, and it is one of the cheapest on the bike.
07 — Hall error. The hall connection inside the motor cable. Start at the motor connector rather than at the motor. A corroded or pushed-back pin looks identical to a dead sensor from the controller’s point of view, and it costs nothing to inspect.
What codes 08 through 99 mean
The manuals list 08 through 99 as reserved and tell you to contact the manufacturer. That is worth taking literally. A number in that range is not a documented fault with a documented fix, so treat it as unidentified rather than looking for a meaning that the manual does not give it. If a builder or a brand has loaded custom firmware, they are the only reliable source for what a reserved number means on that particular bike.
Where this table comes from
These seven entries are transcribed from two display manuals published by display manufacturers, not from any bike brand’s service documentation. That distinction matters. A brand that fits this display can define its own behaviour in its own manual, and where the two disagree, the document that came with your bike wins. We have not invented entries to round the table out, and any code you see that is not one of these seven is a code we cannot explain for you.
02 and 03: check the connector before the parts
Both of these codes point at the three phase wires, and both are commonly caused by the connection rather than by the controller or the motor. Disconnect the main motor connector, look into both halves under good light for a pin that sits lower than its neighbours, and look for green or white residue that indicates water has been in there. Reseat it firmly and retest before ordering anything. If the code survives a clean, properly seated connection, then you are into component testing.
Which part to replace when the code is a communication fault
Code 01 is the one where people replace the wrong thing. The sequence that wastes the least money is to rule out the cable and connector first, then substitute the display, then the controller, because a display is normally the cheaper of the two. If a known-good display of the same protocol still reports 01, the fault is on the controller side or in the wiring between them. Our guide to why a new display may not work with your controller covers why matching connectors do not guarantee a matching protocol.
Displays from other families number their faults on completely different scales, so do not carry this table across. The SW900 table starts at zero and includes several numbers that are not faults at all, and the KT-LCD table uses a different range again. Read the code against the display you actually have.