The display is black, or it is showing a number you have never seen, and there is a couple in helmets waiting. You do not owe them a diagnosis. You owe them a bike that goes, or an honest no. The three things worth doing while they watch Is the battery seated, and is it charged? A display with no pack behind it looks exactly like a dead computer. Pull the battery off, put it back until it clicks, and try the button again. A lot of "dead" bikes are a pack that was on the charger and never quite latched. Is the cable clicked in? The short lead between the display and the bike gets bumped by a handlebar bag, a lock, a child. Unplug it, look for a bent pin, plug it back. If the pin is bent, stop. That bike is not going out, and forcing the plug is how a small fault becomes a loom. Does a different battery from the same fleet wake it? If yes, the pack or that pack's connection is the problem, and you have learned something useful. If no, swap the whole bike. Write the number down. The guest leaves. That is the whole counter routine. It should take a few minutes. Anything longer and you are repairing in public, which is how both the guest and the bike have a bad morning. The code, afterwards Bosch, Shimano, Brose, Giant, Specialized: they do not share a list of numbers. A code is a sentence in that brand's manual. Photograph the screen before you clear it. Look up that brand, that year, that code. A page that lists forty codes for every motor on earth is how you replace a sensor the bike does not have. Some codes mean "charge the battery." Some mean "don't ride this until a dealer sees it." You cannot tell from the number of digits. If the manual says dealer, it is a dealer. Clearing the code so the bike will hire this afternoon, without reading what it meant, is how the same bike comes back on a truck. A display that is simply missing, prised off overnight, is theft plus a bike you cannot hire until it is replaced. Do not jury-rig a phone app unless that motor is actually built to run from the phone and you have done it before. Most fleets are not. What you tell the guest The first bike had a fault and you are not sending them out on it. The second bike is ready. If you are down to the last bike and it is the broken one, say so before you take the money. A dead display is annoying. A guest who finds out at the rack is a review. The tour they were going to ride still exists. The bike changed, the day didn't have to. If the replacement is a different kind of bike, an e-bike for a pushbike or the other way around, the time and the hill change with it. Say the new time out loud. The tour can re-quote a day from the bike you hand over. Use that, rather than hoping they will be back before the boat.